Lithium-sulfur battery
As the representative of the next generation of high energy density energy storage technology, lithium-sulfur (Li-S) battery is leading a new revolution in the field of energy storage. Compared with the current mainstream lithium-ion batteries, lithium-sulfur batteries are regarded as an ideal choice to solve the range anxiety of electric vehicles and the energy needs of aerospace due to their ultra-high theoretical energy density (2600Wh/kg), lightweight characteristics and low cost advantages. This article will comprehensively analyze the technical principles, significant advantages, key challenges and latest research breakthroughs of lithium-sulfur batteries, show how this technology has moved from the laboratory to industrial application, and explore its future development direction. From sulfur cathode material modification to electrolyte innovation, from interface engineering to all-solid-state design, scientists are overcoming the commercialization barriers of lithium-sulfur batteries through multidisciplinary cross-research, providing strong technical support for the clean energy transition.
1. Overview of lithium-sulfur battery technology
Lithium-sulfur battery is a new type of electrochemical energy storage system with sulfur as the positive electrode and metallic lithium as the negative electrode. Its working principle is fundamentally different from that of traditional lithium-ion batteries. In lithium-sulfur batteries, the energy storage mechanism is based on the multi-step electrochemical conversion reaction between sulfur and lithium, rather than the embedding/de-embedding process of lithium ions in electrode materials. When the battery is discharged, the metallic lithium negative electrode loses electrons to form lithium ions, while the sulfur positive electrode reacts with lithium ions and electrons to generate lithium polysulfide (Li₂Sₙ, 1≤n≤8), which is finally converted into lithium sulfide (Li₂S); the charging process is reversed, so that lithium sulfide is converted back into sulfur. This unique reaction mechanism gives lithium-sulfur batteries a theoretical energy density far exceeding that of traditional lithium-ion batteries.
From the perspective of structural composition, a typical lithium-sulfur battery contains the following key components: a metallic lithium negative electrode as a lithium source, usually in the form of lithium foil or lithium alloy; a sulfur-based positive electrode, usually composed of sulfur and conductive carbon materials to improve the conductivity and structural stability of sulfur; an electrolyte system, which is mostly an ether organic electrolyte in liquid lithium-sulfur batteries, and a sulfide or oxide solid electrolyte in all-solid-state designs; and a separator to prevent the positive and negative electrodes from directly contacting each other and causing a short circuit. In recent years, researchers have also introduced functional interlayers or interlayers between the positive and negative electrodes to inhibit the shuttle effect of polysulfides and improve battery performance.
The electrochemical reaction process of lithium-sulfur batteries is far more complex than that of traditional lithium-ion batteries. During the discharge process, the sulfur positive electrode undergoes a multi-step transformation from S₈ cyclic molecules to long-chain polysulfides (Li₂S₈, Li₂S₆, etc.), to short-chain polysulfides (Li₂S₄, Li₂S₂), and finally to Li₂S. This process is accompanied by significant volume changes (about 80%) and complex phase change behaviors. At the same time, the dissolution and migration of the intermediate product lithium polysulfide will lead to loss of active materials and "shuttle effect", which is one of the main factors affecting the cycle life of the battery.
Compared with traditional lithium-ion batteries, lithium-sulfur batteries have many inherent advantages. The first is the energy density advantage - the theoretical mass specific capacity of sulfur is as high as 1675mAh/g, and that of lithium is 3860mAh/g. The theoretical energy density of the combination of the two can reach 2600Wh/kg, which is 5-8 times that of existing lithium-ion batteries (about 300Wh/kg). In practical applications, the energy density of lithium-sulfur batteries reported so far has reached 700Wh/kg, which is 2-3 times that of commercial lithium-ion batteries. The second is the cost advantage - sulfur is one of the most abundant elements on earth, with low price and wide distribution, avoiding the dependence of lithium-ion batteries on expensive transition metals such as cobalt and nickel. The third is environmental friendliness - lithium-sulfur batteries do not contain heavy metals, have low toxicity, and are more in line with the concept of sustainable development. In addition, lithium-sulfur batteries also have wide temperature range performance. They can still charge and discharge at -50℃ to -40℃, and can also discharge stably at -70℃ to -100℃, which can adapt to extreme environmental applications.
These characteristics of lithium-sulfur batteries make them show great potential in multiple application fields. In the field of electric vehicles, lithium-sulfur batteries can easily exceed 1,200 kilometers in range, or even reach 2,000 kilometers, fundamentally solving the "range anxiety". In the field of aerospace, its high energy density and lightweight characteristics can significantly improve the performance of aircraft. Studies have shown that it can be used in electric vertical take-off and landing aircraft (eVTOL) and satellite systems. In portable electronic devices and large-scale energy storage systems, lithium-sulfur batteries have also attracted attention for their long range and safety characteristics. As the technology continues to mature, lithium-sulfur batteries are moving from laboratories to industrialization, and are expected to reshape the global energy storage landscape.
2. Significant advantages of lithium-sulfur batteries
The reason why lithium-sulfur battery technology is regarded as a revolutionary breakthrough in the field of energy storage is due to its series of outstanding performance advantages that surpass traditional lithium-ion batteries. These advantages are not only reflected in theoretical calculations, but also verified in experimental research and preliminary commercial applications in recent years, bringing unprecedented possibilities to multiple industries.
Ultra-high energy density is the most striking feature of lithium-sulfur batteries. From a theoretical point of view, the mass specific capacity of the sulfur positive electrode is as high as 1675mAh/g, and the lithium negative electrode is as high as 3860mAh/g. The theoretical energy density of the combination of the two can reach 2600Wh/kg. This value is 5-8 times that of current commercial lithium-ion batteries (generally in the range of 250-300Wh/kg). In practical applications, although it is limited by various factors and cannot fully reach the theoretical value, the leading research team has achieved a major breakthrough. The energy density of lithium-sulfur batteries developed by Anhui Tongneng New Energy Technology Co., Ltd. has reached 700Wh/kg, which is 2-3 times that of existing lithium-ion batteries. The first generation of commercial lithium-sulfur batteries developed by German battery research institute Theion has an energy density of 500Wh/kg, and plans to launch a third-generation product with an energy density of up to 1000Wh/kg in 2024. This leap in energy density means that lithium-sulfur batteries can store and release more electricity at the same weight or volume, fundamentally changing the economics and practicality of energy storage.
In electric vehicle applications, the energy advantage of lithium-sulfur batteries translates into a revolutionary increase in driving range. Currently, electric vehicles equipped with lithium iron phosphate or ternary lithium batteries generally have a driving range of 400-600 kilometers, but with the use of lithium-sulfur battery technology, this number can easily exceed 1,200 kilometers or even reach 2,000 kilometers. This means that daily commuting may only require charging once every two weeks, and long-distance travel will no longer be troubled by charging frequency. For the popularization of electric vehicles, this qualitative change in driving range will completely eliminate consumers' "mileage anxiety" and make electric vehicles truly comparable to or even surpass traditional fuel vehicles in practicality. It is worth noting that the high energy density of lithium-sulfur batteries is also accompanied by the advantage of weight reduction, which has dual benefits for vehicle energy efficiency and performance improvement.
Cost advantage is another key competitive advantage of lithium-sulfur batteries. Sulfur is one of the most abundant elements on earth, with an extremely low price (about US$0.25/kg), and the mining and purification process is relatively simple. In contrast, traditional lithium-ion battery cathode materials such as lithium cobalt oxide (LCO) and lithium nickel cobalt manganese oxide (NMC) rely on scarce and volatile transition metals (cobalt costs about $30/kg and nickel costs about $15/kg). Lithium-sulfur batteries do not require these expensive materials, which can theoretically significantly reduce battery costs. In addition, lithium-sulfur batteries are charged after assembly, while traditional lithium batteries need to be activated and charged for the first time after assembly, which simplifies the production process and reduces manufacturing costs. Although the current manufacturing cost of lithium-sulfur batteries is still relatively high (mainly limited by the maturity of technology and production scale), with technological progress and large-scale production, its cost advantage will become increasingly prominent. Some analysts point out that once large-scale production is achieved, the cost of lithium-sulfur batteries may be 30-50% lower than that of existing lithium-ion batteries, which will greatly promote the popularization of electric vehicles and energy storage systems.
Lithium-sulfur batteries also show unique advantages in environmental adaptability. Studies have shown that lithium-sulfur batteries can still maintain good performance under extreme temperature conditions, can be charged and discharged normally between -50℃ and -40℃, and can also discharge stably in ultra-low temperature environments of -70℃ to -100℃. This feature makes it particularly suitable for special environmental applications such as aerospace and polar expeditions. In contrast, the performance of traditional lithium-ion batteries drops sharply at low temperatures, and the capacity may decay by more than 50% at -20℃. The amorphous bimetallic polysulfide Mo0.5Ti0.5S4 positive electrode material developed by Wu Fan's team at the Institute of Physics, Chinese Academy of Sciences, has a capacity retention rate of 50.5% at -20℃ and can still maintain a capacity of 35.1-50.7% at -40℃, showing excellent low-temperature performance. This wide temperature range performance not only expands the application scenarios of the battery, but also improves its reliability in the context of climate change.
Fast charging capability is an important breakthrough direction for lithium-sulfur batteries in recent years. The traditional view is that the rate performance of lithium-sulfur batteries is limited, but the latest research shows that by optimizing the electrolyte and electrode design, charging speeds close to those of lithium-ion batteries can be achieved. The all-solid-state lithium-sulfur battery developed by Quanquan Pang's team at Peking University releases a high specific capacity of 1497mAh/g at a 2C rate, and even when charged at an ultra-high rate of 20C, the capacity can still reach 784mAh/g. Even more impressive is that the battery still maintains 80.2% of its initial capacity after 25,000 cycles at a 5C rate at 25°C, showing ultra-long cycle life and fast charging stability. Professor Quanquan Pang said: "Compared with the hour-level charging capacity and thousand-cycle life of existing lithium-ion batteries, all-solid-state lithium-sulfur batteries are expected to achieve minute-level fast charging and ten thousand-cycle charging." This fast charging feature is crucial for the practical application of electric vehicles, which can greatly shorten the charging waiting time and improve the user experience.
The safety performance of lithium-sulfur batteries is also better than that of traditional lithium-ion batteries. On the one hand, the working potential of the sulfur positive electrode is moderate (about 2.1V vs. Li+/Li), which will not cause excessive decomposition or oxygen release of the electrolyte, reducing the risk of thermal runaway. On the other hand, lithium-sulfur batteries using solid electrolytes completely eliminate flammable organic liquid electrolytes, fundamentally solving the hidden dangers of combustion and explosion. Research from Peking University shows that all-solid-state lithium-sulfur batteries "do not release oxygen during charging, so they have higher intrinsic safety." In addition, lithium-sulfur batteries also have better thermal stability in the case of overcharging or mechanical damage, which is particularly important for electric vehicles and aviation applications.
These advantages of lithium-sulfur batteries do not exist in isolation, but are interrelated and mutually reinforcing. The combination of high energy density and lightweight can further improve energy efficiency; the combination of low cost and environmental protection characteristics is in line with the sustainable development strategy; the combination of fast charging capability and long cycle life improves economy and practicality. With the deepening of research and the maturity of technology, lithium-sulfur batteries are moving from laboratories to industrialization, from special applications to the mass market, and are expected to reshape the pattern of energy storage and utilization, and provide strong technical support for the clean energy transition.
3. Current technical challenges
Although lithium-sulfur batteries have many attractive advantages, their commercialization process still faces multiple technical barriers. These challenges involve multiple fields such as materials science, electrochemistry, and interface engineering, and require interdisciplinary collaboration to overcome. A deep understanding of these technical bottlenecks is crucial to promoting lithium-sulfur batteries from the laboratory to industrialization.
The shuttle effect of polysulfides is one of the most prominent problems of lithium-sulfur batteries. During the operation of the battery, the intermediate product lithium polysulfide (Li₂Sₙ, 4≤n≤8) generated at the positive electrode is easily soluble in the organic electrolyte to form soluble polysulfides. These dissolved species will migrate between the positive and negative electrodes: on the one hand, polysulfides that migrate from the positive electrode to the electrolyte cause the loss of active substances; on the other hand, polysulfides that migrate to the surface of the lithium negative electrode will react irreversibly with metallic lithium to form an electronically insulating Li₂S/Li₂S₂ layer, consuming active lithium and electrolyte. This phenomenon is called the "shuttle effect", which not only causes the battery capacity to decay rapidly, but also leads to low Coulomb efficiency and severe self-discharge. Studies have shown that lithium-sulfur batteries with traditional liquid electrolytes may lose 1-5% of their capacity per day due to the shuttle effect during the cycle, which seriously limits their cycle life. Even with advanced electrolyte formulations, the shuttle effect is still the main factor affecting the long-term stability of lithium-sulfur batteries.
The insulating properties of sulfur and its discharge products pose another major challenge. The conductivity of elemental sulfur at 25°C is only about 10⁻³⁰ S/cm, and the conductivity of the discharge end product Li₂S is only about 10⁻¹³ S/cm, both of which are typical electronic insulators. This extremely low conductivity seriously hinders the electrochemical reaction, resulting in low sulfur utilization and poor rate performance. In actual battery design, sulfur must be composited with highly conductive materials (such as porous carbon, graphene, carbon nanotubes, etc.) to construct an electronic conduction network. However, even with these strategies, the kinetic performance of the sulfur cathode is still not ideal, especially under high sulfur loading and poor electrolyte conditions, the internal resistance of the battery will increase significantly and the performance will drop sharply. Wu Fan's team from the Institute of Physics, Chinese Academy of Sciences, pointed out that "the insulating properties of elemental sulfur and the discharge product Li₂S" are one of the key factors restricting the performance of lithium-sulfur batteries.
The volume change during charging and discharging poses a severe test to battery design and long-term stability. When sulfur is converted to Li₂S, the density changes from 2.03g/cm³ to 1.66g/cm³, accompanied by a volume expansion of about 80%. This huge volume change can lead to the destruction of the positive electrode structure, the breakage of the conductive network, and the separation of the electrode and the current collector, which in turn causes the inactivation of the active material and capacity decay. On a macro scale, repeated volume changes can also cause the battery shell to be subjected to periodic stress, which may cause problems such as electrolyte leakage or poor interface contact. In contrast, the volume change of traditional lithium-ion battery electrode materials is usually less than 10%, so the mechanical stability challenges faced by lithium-sulfur batteries are more severe. How to design an electrode structure that can adapt to such large volume changes is one of the key issues in the research and development of lithium-sulfur batteries.
The instability of the lithium negative electrode is another bottleneck restricting the performance of lithium-sulfur batteries. Metallic lithium has the highest theoretical capacity (3860mAh/g) and the most negative electrochemical potential (-3.04V vs. SHE), making it an ideal negative electrode material, but it also has many problems. First, lithium reacts with the electrolyte (especially dissolved polysulfides) to form an unstable solid electrolyte interface (SEI) layer, which continuously consumes active lithium and electrolyte. Second, during the electroplating/stripping process, lithium tends to form dendritic deposits, and these lithium dendrites may pierce the diaphragm and cause short circuits, posing safety hazards. In addition, the infinite volume change and interface instability of the lithium negative electrode during the cycle also greatly affect the cycle life of the battery. The team of Quanquan Pang of Peking University pointed out: "The poor stability of the Li/electrolyte interface may cause safety hazards." Even in solid-state lithium-sulfur batteries, the interface problem of the lithium negative electrode still exists and requires special attention.
The limitation of the electrolyte system is also an important challenge facing lithium-sulfur batteries. In traditional liquid lithium-sulfur batteries, although ether electrolytes can dissolve polysulfides well and promote reaction kinetics, they also aggravate the shuttle effect. Although carbonate electrolytes can inhibit the dissolution of polysulfides, they are prone to irreversible reactions with polysulfides, resulting in battery failure. In addition, under poor electrolyte conditions (E/S ratio <5μL/mg), the viscosity of the electrolyte increases, ion transport is hindered, and polysulfides are easy to agglomerate, resulting in low sulfur utilization and poor cycle stability. Under low temperature conditions, the electrolyte may gel, further deteriorating battery performance. Although solid electrolytes can solve many problems of liquid electrolytes, they face new challenges of poor interface contact and slow solid-solid reaction kinetics. Professor Wang Donghai's team at Pennsylvania State University pointed out: "The solid sulfur conversion reaction kinetics are slow and are mainly limited by the influence of the three-phase contact of the interface between sulfur, carbon and solid electrolyte."
The balance between cycle life and energy efficiency is a key obstacle to the commercialization of lithium-sulfur batteries. Although lithium-sulfur batteries have extremely high energy density in theory, in practical applications, some energy density needs to be sacrificed in exchange for cycle stability. For example, measures such as using excess lithium anodes, large amounts of electrolytes, or low sulfur loading can improve cycle performance but reduce overall energy density. At present, the cycle life of lithium-sulfur batteries studied in most laboratories is between 100-500 times, which is far below the commercial requirements (>1000 times). Even for batteries with better performance, such as the lithium-sulfur battery with an intermediate layer developed by Monash University in Australia, although it can achieve 2000 cycles, its energy density may have been greatly reduced. How to improve the cycle life without significantly sacrificing energy density is the core challenge of lithium-sulfur battery research and development.
Limited low-temperature performance is another challenge faced by lithium-sulfur batteries in special application scenarios. Although lithium-sulfur batteries have a wide operating temperature range in theory, under actual low-temperature conditions (<-10°C), the reaction kinetics slow down significantly, polysulfide agglomeration intensifies, and the electrolyte ion conductivity decreases, resulting in a sharp deterioration in battery performance. Especially under poor electrolyte conditions, the low-temperature performance degradation is more serious, which limits the application of lithium-sulfur batteries in low-temperature environments such as aerospace and polar scientific research. Research on high-entropy electrolytes shows that the ionic conductivity of traditional electrolytes at -15°C may be less than 1/10 of that at room temperature, which seriously affects battery output. Even with solid electrolytes, ion transport and interface reaction problems at low temperatures still exist.
These technical challenges are interrelated and mutually influential, constituting multiple obstacles to the commercialization of lithium-sulfur batteries. The shuttle effect and lithium anode problems together lead to short cycle life; insulation properties and electrolyte limitations together restrict rate performance; volume changes and interface problems together affect structural stability. Solving these problems requires systematic innovation rather than isolated material or process improvements. Fortunately, significant progress has been made in recent years in material design, interface engineering, and system optimization, providing a variety of feasible paths to overcome these challenges. These breakthroughs will be discussed in detail in the next section.
4. Innovative breakthroughs to overcome technical obstacles
Faced with multiple challenges on the road to commercialization of lithium-sulfur batteries, global scientific research teams have made a series of breakthroughs in materials science, electrochemistry and engineering. These innovations cover multiple aspects such as cathode design, electrolyte engineering, interface optimization and system integration, which significantly improve the performance and reliability of lithium-sulfur batteries and lay a solid foundation for their industrial application.
Innovation of cathode materials and structures
Sulfur host material design is the core strategy to improve cathode performance. Traditional methods load sulfur into porous carbon materials to improve conductivity and limit polysulfides, but the effect is limited. In recent years, researchers have developed a variety of new host materials, such as the graphene-sulfur composite material jointly developed by the Institute of Metal Research, Chinese Academy of Sciences and Xinjinlu Group, which effectively binds sulfur species and promotes electron transport through the high conductivity and rich pores of graphene. The team of He Gaohong and Li Xiangcun from Dalian University of Technology constructed a carbon nanofiber membrane (Cu-CeO₂₋ₓ@CNF) loaded with a Cu-CeO₂₋ₓ heterostructure as an interlayer between the positive electrode and the separator. This design not only provides a highly conductive continuous carbon skeleton, but the oxygen vacancies on its heterogeneous interface can also catalyze the conversion of polysulfides, reduce the reaction energy barrier, and enable the battery to maintain a capacity of 626mAh/g after 800 cycles at a current density of 2C, with a decay rate of only 0.046% per cycle.
Amorphous bimetallic polysulfides represent another innovative direction for positive electrode materials. The Mo₀.₅Ti₀.₅S₄ material developed by Wu Fan's team at the Institute of Physics, Chinese Academy of Sciences, breaks through the limitations of crystalline materials. The study found that the introduction of Ti reduced the elastic modulus, accelerated the amorphization during ball milling, and increased the active sites and inhibited the S/Li₂S phase separation. Compared with MoS₄, the specific capacity of Mo₀.₅Ti₀.₅S₄ has been significantly improved from 757mAh/g to 914mAh/g, and the capacity retention rate at 4C has been increased from 47.2% to 65.8%. More notably, the material exhibits excellent low-temperature performance, with a capacity retention rate of 50.5% at -20°C and a capacity of 35.1-50.7% at -40°C, which makes it possible for applications in extreme environments. This design concept of amorphous bimetallic polysulfides has opened up new avenues for the development of high-capacity, low-temperature-resistant sulfur-equivalent positive electrodes.
The construction of a three-dimensional conductive network is an effective means to improve sulfur utilization and rate performance. Professor Wang Donghai's team at Pennsylvania State University used mixed ion-electron conductors (MIECs) to replace traditional solid-state electrolytes, overcoming the three-phase interface limitations. Microscopic analysis shows that a mixed conductive domain embedded in sulfur is formed at the sulfur-MIEC boundary, promoting the complete conversion of active sulfur into Li₂S. This design enables the sulfur utilization rate of all-solid-state lithium-sulfur batteries to reach 87.3%, the conversion rate >94%, the discharge capacity >1450mAh/g, and the cycle life of more than 1000 times. Professor Wang Donghai pointed out that this strategy "not only provides a new perspective for the study of electrode interfaces in solid-state batteries, but also provides an effective strategy to overcome the interface conversion reaction limitations of conversion-type cathodes in ASSBs."
Breakthrough progress in electrolyte systems
High-entropy electrolyte design provides a new idea for solving performance bottlenecks under poor electrolyte and low temperature conditions. The latest research has developed a high-entropy (HE) electrolyte composed of three lithium salts of equimolar LiFSI, LiTFSI and LiBETI and LiNO₃ additives. This electrolyte breaks the limitations of traditional design through entropy regulation strategies and significantly improves performance at low E/S ratios (3μL/mg) and -15℃. Mechanistic studies have shown that HE electrolytes can reduce the size of LiPS clusters, promote lithium ion diffusion (self-diffusion coefficient increased by 26.3%), and build a strong anion-derived SEI layer. The initial reversible capacity of the battery using HE electrolyte reached 1159.9mAh/g, and it was stably cycled 200 times at -15℃ with a capacity decay rate of only 0.01%. This high entropy design concept breaks through the limitations of traditional electrolyte formulations and provides a solution for lithium-sulfur batteries used under extreme conditions.
All-solid-state electrolytes are the fundamental way to improve safety and cycle stability. In a study published in Nature, the research group of Quanquan Pang of Peking University designed and synthesized a glassy phase sulfide LBPSI electrolyte (Li₂S-B₂S₃-P₂S₅-LiI) with high ionic conductivity. This material not only acts as a superionic conductor, but the redox-active iodine element it contains also mediates the solid-solid conversion of sulfur, significantly increasing the density of active sites. The all-solid-state lithium-sulfur battery based on this electrolyte exhibits excellent fast charging performance (capacity of 784mAh/g at 20C rate) and ultra-long cycle life (capacity retention rate of 80.2% after 25,000 cycles at 5C). Professor Pang Quanquan vividly compared it to the intelligent self-driving car of the future. On the premise of achieving the basic function of transportation, it not only saves the fatigue of long-distance driving, but also allows you to rest in the car. This breakthrough has made all-solid-state lithium-sulfur batteries take a key step towards the goal of "minute-level fast charging and 10,000 cycles of charging".
Interface engineering is also crucial to improving the performance of all-solid-state lithium-sulfur batteries. In traditional solid-state batteries, the poor solid-solid interface contact leads to the obstruction of ion transmission, and the interface side reactions affect the stability. To address this problem, researchers have developed a variety of interface optimization strategies.
The Peking University team designed the electrolyte to allow iodine to participate in redox mediation, activating the SE|Li-S two-phase interface reaction that was originally difficult to carry out. They used time-of-flight secondary ion mass spectrometry to confirm the reversible redox behavior of iodine in the battery and revealed the mechanism of enhanced interface reaction. On the other hand, by constructing a gradient interface layer or applying stacking pressure, the interface contact can be improved and the growth of lithium dendrites can be inhibited. These breakthroughs in interface engineering have significantly reduced the interface impedance of all-solid-state lithium-sulfur batteries and greatly improved the reaction kinetics, clearing the way for their practical application.
Strategies to inhibit the shuttling effect of polysulfides
Functional membranes and interlayers are effective means to inhibit the shuttling effect. Researchers at the University of Michigan have developed a biomimetic membrane made of recycled Kevlar fibers that selectively allows lithium ions to pass through while blocking polysulfides. This design allows lithium-sulfur batteries to approach full potential in terms of capacity and number of cycles, withstand more than 1,000 cycles, and are not affected by extreme temperatures. Monash University in Australia has introduced a new lithium-sulfur battery interlayer, which is located in the middle of the battery to help lithium transfer quickly while preventing polysulfides from moving. Lithium batteries with this interlayer can achieve 2,000 charge and discharge cycles without failure, which is significantly better than traditional designs. These physical barrier methods are relatively low-cost, easy to scale up, and have good commercial prospects.
Catalyst design accelerates polysulfide conversion and reduces soluble species from the source. The Cu-CeO₂₋ₓ heterogeneous interface constructed by the Dalian University of Technology team increased the oxygen vacancy content, changed the band structure, and caused orbital hybridization between atoms and the disappearance of the band gap. This characteristic reduces the reaction energy barrier of the catalytic process, accelerates the catalytic conversion of polysulfides and the decomposition of Li₂S. Similarly, the introduction of Ti in the amorphous bimetallic polysulfides developed by the Chinese Academy of Sciences team also increases the active sites and promotes the reaction kinetics. These catalytic strategies not only suppress the shuttle effect, but also improve the sulfur utilization rate and rate performance, achieving the effect of "killing two birds with one stone".
Electrolyte additives are a clever solution to balance shuttle inhibition and reaction kinetics. In liquid electrolytes, the addition of substances such as LiNO₃ can form a protective film on the surface of the lithium negative electrode, reducing the reaction of polysulfides with lithium. The synergistic effect of various lithium salts in high-entropy electrolytes can not only regulate the dissolution behavior of LiPS, but also stabilize the SEI layer. The active iodine element (I⁻/I₂/I₃⁻) in the all-solid electrolyte plays a dual role, both conducting ions and mediating reactions, fundamentally changing the interface reaction mechanism. These additive strategies significantly improve battery performance at a lower cost and have high practical value.
Advances in lithium anode protection technology
Solid electrolyte interface (SEI) engineering is the key to stabilizing lithium anodes. Studies have shown that the SEI layer (20.5nm) formed by high entropy electrolytes is thinner than that formed by traditional electrolytes (26.9nm) and rich in inorganic components (Li₂O, LiF), which effectively inhibits electrolyte decomposition. XPS depth analysis shows that the SEI layer formed by HE electrolytes has lower organic content and higher (F+N)/C atomic ratio, indicating that it is more stable and durable. This strong anion-derived SEI layer enables lithium symmetric batteries to cycle stably within 400 hours, while the overpotential of traditional systems increases significantly after 300 hours. Regulating SEI properties through electrolyte component design has become one of the mainstream strategies for protecting lithium anodes.
Three-dimensional lithium host structures can guide uniform lithium deposition and inhibit dendrite growth. Researchers have designed a variety of porous conductive skeletons (such as carbon fiber networks, metal foams, etc.) as lithium deposition carriers. These structures provide huge specific surface area, reduce local current density, and buffer volume changes. In-situ SEM observations show that in the optimized electrolyte system, the lithium deposition morphology is more dense and uniform, reducing the risk of dendrite formation. Combined with measures such as applying external pressure, the three-dimensional host structure can significantly improve the cycle stability and safety of the lithium negative electrode.
The alloying strategy improves the negative electrode performance by forming a lithium alloy. Adding elements such as magnesium and aluminum to lithium to form an alloy can improve the mechanical strength and reduce the reaction activity. The alloy negative electrode has a higher melting point and better dimensional stability, and can resist dendrite growth and volume fluctuations. Although alloying will slightly reduce the theoretical capacity, it will significantly improve safety and cycle life. This trade-off is worthwhile in some application scenarios. With the advancement of material design and preparation technology, high-performance lithium alloy negative electrodes are gradually becoming practical.
These innovative breakthroughs do not exist in isolation, but support and promote each other. The advancement of positive electrode materials requires a matching electrolyte system; the optimization of interface engineering is inseparable from a deep understanding of the reaction mechanism; lithium negative electrode protection and polysulfide control strategies need to be designed in a coordinated manner. It is this multi-dimensional and systematic innovation that has driven lithium-sulfur battery technology to overcome obstacles and steadily move towards industrial application. As these technologies gradually mature and move towards integration, the commercial prospects of lithium-sulfur batteries are becoming clearer and clearer, and are expected to be widely used in the next 5-10 years, reshaping the energy storage landscape.
5. Application prospects and future development direction
After years of development, lithium-sulfur battery technology has gradually moved from laboratory research to the threshold of industrial application. Its excellent energy density characteristics, continuously improving cycle life and significant cost advantages have enabled it to show transformative potential in many fields. At the same time, with the deepening of research and the development of technology, the future evolution path of lithium-sulfur batteries has become increasingly clear.
Diversified application scenario expansion
The electric vehicle field is regarded as the application market with the most disruptive potential for lithium-sulfur batteries. At present, electric vehicles generally face the problem of "range anxiety". Even the most advanced lithium-ion batteries are difficult to achieve an actual range of more than 600 kilometers under the premise of controllable costs. The industrialization of lithium-sulfur batteries will completely change this situation. The lithium-sulfur battery with an energy density of 700Wh/kg developed by Anhui Tongneng New Energy Technology Co., Ltd. can easily exceed 1,200 kilometers in range for electric vehicles. The third-generation lithium-sulfur battery that the German company Theion plans to launch will have an energy density of 1,000Wh/kg, and the range of electric vehicles equipped with this battery is expected to exceed 2,000 kilometers. This ultra-long range will fundamentally eliminate consumers' range anxiety and make electric vehicles surpass fuel vehicles in practicality. It is worth noting that the lightweight characteristics of lithium-sulfur batteries can further reduce the weight of the vehicle, improve energy efficiency, and form a virtuous circle. Foreign media reported that Toyota plans to launch electric models using lithium-sulfur batteries in 2027 or 2028, marking the recognition of this technology by mainstream car companies.
Aerospace is another important application direction for lithium-sulfur batteries. Aircraft are extremely sensitive to the weight of the energy system, and the energy density of traditional lithium-ion batteries is difficult to meet the needs of electric aviation. The high energy density (500-1000Wh/kg) and wide temperature range performance (-50℃ to 60℃) of lithium-sulfur batteries make them an ideal power source for electric vertical take-off and landing aircraft (eVTOL), drones and satellites. High-entropy electrolyte research shows that lithium-sulfur batteries can still maintain excellent performance under poor electrolyte and low temperature conditions, which is particularly important for aviation applications in high-altitude and low-temperature environments. The amorphous bimetallic polysulfide developed by the Institute of Physics of the Chinese Academy of Sciences can still maintain 50.7% of its capacity at -40℃, showing excellent low-temperature adaptability8. In the aerospace field, the high energy density of lithium-sulfur batteries can significantly extend the mission life of satellites and deep space probes, and its all-solid-state design without volatile components is more suitable for vacuum environments. With the rapid development of urban air traffic (UAM) and low-altitude economy, the market demand for lithium-sulfur batteries will grow rapidly.
Portable electronic devices are another potential market for lithium-sulfur batteries. Smartphones, laptops, wearable devices, etc. have a continuous demand for thin and light batteries and long battery life. The high capacity characteristics of lithium-sulfur batteries can make devices smaller and last longer, and the use time of a single charge can be extended by 2-3 times. The all-solid-state lithium-sulfur battery developed by Peking University has fast charging characteristics and ultra-long cycle life, which is very suitable for consumer electronics applications. Professor Pang Quanquan pointed out: "This achievement will have a profound impact in many fields such as the next generation of automotive power batteries, low-altitude flight power, and high-end electronic batteries." Although the current consumer electronics market is highly sensitive to cost, as the scale of lithium-sulfur batteries expands and the cost decreases, its penetration in this field will gradually increase.
Large-scale energy storage systems may also become an important application scenario for lithium-sulfur batteries. With the increase in the proportion of renewable energy, the demand for grid-level energy storage is growing rapidly. The low cost (thanks to the abundant reserves of sulfur) and high energy density of lithium-sulfur batteries make them competitive in the field of energy storage. In particular, the high safety and long life characteristics of all-solid-state lithium-sulfur batteries are very suitable for energy storage applications. The application prospects of lithium-sulfur battery technology listed by the Ordos Science and Technology Achievement Transformation Platform include "large-scale energy storage systems", which are considered to "improve the efficiency and reliability of energy storage". Although cycle life and calendar life are still challenges at present, with technological advances, lithium-sulfur batteries are expected to occupy a place in specific energy storage scenarios.
Industrialization process and commercialization path
The industrialization of lithium-sulfur batteries has begun to take shape, and many companies and research institutions around the world are promoting it from the laboratory to the market. Many research institutes of the Chinese Academy of Sciences (such as the Institute of Metal Research and Ningbo Institute of Materials) have cooperated with the industry to carry out pilot production and application research and development of lithium-sulfur batteries. The high-energy-density lithium-sulfur battery cells (300-500Wh/kg) developed by the Suzhou Institute of Nanotechnology and Nano-Bionics have cooperated with well-known domestic automobile companies to develop automotive battery packs. Anhui Tongneng New Energy Technology Co., Ltd. has successfully developed a lithium-sulfur battery with an energy density of 700Wh/kg, marking China's leading position in this field. Overseas, Germany's Theion plans to use lithium-sulfur batteries with an energy density of 1000Wh/kg for electric vehicles in 2024, and Toyota also plans to launch lithium-sulfur electric vehicles in 2027-2028.
The commercialization of lithium-sulfur batteries is likely to follow a phased and scenario-based path. The initial applications will focus on special fields with high added value and weight sensitivity, such as aerospace, military applications, etc. The first generation of commercial lithium-sulfur batteries (500Wh/kg) from Germany's Theion were first used in the aviation field. As the technology matures and costs decrease, it will gradually expand to the high-end electric vehicle market. Finally, when the cycle life and fast charging performance are further improved, it will enter the consumer electronics and energy storage markets on a large scale. This gradual commercialization path ensures that technical risks are controllable while gradually expanding production scale to reduce costs.
Industrial chain construction is the key to successful industrialization. The large-scale production of lithium-sulfur batteries requires the establishment of dedicated supply chains for sulfur cathode materials, special electrolytes, and lithium anode processing. Compared with traditional lithium-ion batteries, the production process and equipment of lithium-sulfur batteries are also quite different, and special production equipment and process control technology need to be developed. The technical maturity of lithium-sulfur batteries listed by the Ordos Science and Technology Achievement Transformation Platform is "laboratory level", indicating that most technologies have not yet reached the level of industrialization. Promoting industry-university-research cooperation and accelerating pilot-scale expansion and process verification are necessary measures to shorten the industrialization process.
Future research directions and technological breakthroughs
All-solid-state lithium-sulfur batteries are regarded as the mainstream direction of future development. The team of Pang Quanquan of Peking University and the team of Wang Donghai of Pennsylvania State University have made important breakthroughs in this field. The all-solid-state design can fundamentally solve the problems of polysulfide shuttle and electrolyte combustion, and improve safety and cycle life. Future research will focus on further improving the ionic conductivity of solid electrolytes, reducing interface impedance, and optimizing electrode-electrolyte contact. The iodine-containing LBPSI electrolyte developed by Pang Quanquan's team realizes rapid solid-solid sulfur reaction, providing new ideas for the development of all-solid-state lithium-sulfur batteries. The mixed ion-electron conductor interface design of Wang Donghai's team significantly improves sulfur utilization. These innovations will push all-solid-state lithium-sulfur batteries toward the goal of "minute-level fast charging and 10,000 cycles of charging".
Adaptability to low temperature and extreme environments is another important research direction. The amorphous bimetallic polysulfide and high entropy electrolyte research of the Institute of Physics, Chinese Academy of Sciences, have provided new solutions for improving the low-temperature performance of lithium-sulfur batteries. In the future, it is necessary to further explore wide-temperature electrolyte systems, low-temperature active electrode materials, and interface designs that adapt to temperature changes. In particular, for special application scenarios such as aerospace and polar scientific research, it is of great significance to develop -60℃ to 80℃ all-weather lithium-sulfur batteries. The excellent performance of high-entropy electrolytes at -15℃ (the capacity decay rate after 200 cycles is only 0.01%) sets a benchmark for this direction.
Intelligent and structural integrated design will be the development trend of lithium-sulfur batteries in the future. By implanting sensors and intelligent management systems, key parameters such as polysulfide concentration and lithium deposition morphology inside the battery can be monitored in real time to achieve adaptive regulation and predictive maintenance. On the other hand, the integrated design of batteries with vehicle and aircraft structures can further improve the system energy density and space utilization. Structural lithium-sulfur batteries may become the "energy skin" of future electric aircraft, while taking on the dual functions of energy storage and structural support.
Sustainability and circular economy concepts will have a profound impact on the future development of lithium-sulfur batteries. The natural abundance and environmental friendliness of sulfur give lithium-sulfur batteries an inherent sustainable advantage. Future research will focus more on developing green manufacturing processes, recyclable designs, and retired battery regeneration technologies. The University of Michigan's research on using recycled Kevlar fibers to prepare bionic diaphragms is a model of sustainable design. The full life cycle management from raw material mining, battery production, use to recycling will become an important consideration for the development of lithium-sulfur battery technology.
The development of lithium-sulfur battery technology is not isolated, but complements progress in multiple fields such as materials science, manufacturing processes, and system integration. With the development of artificial intelligence, advanced characterization technology, and computational materials science, the research and development efficiency of lithium-sulfur batteries will be further improved, accelerating their commercialization process. In the long run, lithium-sulfur batteries are expected to become an important part of the energy storage field, complementing other technologies such as lithium-ion batteries and solid-state batteries, and jointly promoting global energy transformation and the realization of carbon neutrality goals. As Professor Pang Quanquan said, this technology "provides a new technical solution for the development of next-generation power batteries with high specific energy and high safety." Its impact will go far beyond the battery field itself and will profoundly change our energy utilization and transportation patterns.
