With the continuous development of the global economy, the deepening energy crisis, and the increasing awareness of environmental protection, the power battery industry, as a new energy source and environmentally friendly low-carbon technology, has experienced rapid development. Lithium-ion batteries, with their superior performance and mature technology, have become the mainstream development direction for many power batteries. Lithium-ion batteries mainly consist of a positive electrode, a negative electrode, an electrolyte, and a separator. They function by the movement of lithium ions between the positive and negative electrodes and have the ability to be repeatedly charged. With continuous breakthroughs in material types, performance technologies, and effective control of production costs, the advantages of lithium-ion batteries—lightweight, long driving range, wide applicability, high energy density, and high output power—will gradually become apparent, leading to their development as the primary power battery type and the main type of power battery for today's new energy vehicles.
I. Cathode Materials for Lithium-ion Batteries
Currently, the cathode materials for lithium-ion power batteries used in industrial applications both domestically and internationally include lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, ternary materials (lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide), and lithium nickel oxide. Major manufacturers include Hunan Shanshan New Materials Co., Ltd., Hunan Ruixiang New Materials Co., Ltd., Peking University Pioneer Technology Industry Co., Ltd., Beijing Dangsheng Materials Technology Co., Ltd., Tianjin Bamo Technology Co., Ltd., Ningbo Jinhe New Materials Co., Ltd., and Shenzhen Tianjiao Technology Co., Ltd.
1. Main cathode materials
Lithium cobalt oxide has a capacity of up to 140 mAh/g, is lightweight, small in size, has stable charge and discharge voltage, high conductivity, and simple production process. Preparation methods include high-temperature solid-state method, sol-gel method, precipitation method, spray drying method, and hydrothermal synthesis method. However, the high price of raw materials, poor thermal stability, and serious pollution problems limit its application in electric vehicles.
Lithium nickel oxide has a capacity of 190-210 mAh/g, low environmental pollution and low self-discharge rate, and can be synthesized by high-temperature solid-phase method and sol-gel method; however, it has poor thermal stability and rapid capacity decay.
Lithium manganese oxide is abundant, low-cost, and safe, with spinel and layered structures. Its specific energy ranges from 80 to 120 Wh/kg, and its cycle life is around 1500 cycles. Spinel lithium manganese oxide, with its three-dimensional tunnel structure, better utilizes the insertion and extraction of lithium ions, resulting in lower cost, stable performance, and mature production technology, making it easy to achieve industrial production. However, it suffers from rapid capacity decay and poor high-temperature cycling performance. Layered lithium manganese oxide has a high capacity, reaching 250 mA·h/g, but its cycling performance is poor, it is unstable at high temperatures, and its capacity decay problem is more severe, making industrial production more difficult.
Lithium iron phosphate (LFP) has an olivine-type structure, a specific energy of 100–120 Wh/kg, a cycle life of up to 2000 cycles, good thermal stability and safety, abundant raw materials, low manufacturing cost, and long cycle life, making it widely used in current electric vehicles. However, its relatively low specific energy and specific power limit its application in large pure electric vehicles. Currently, there is a trend towards nano-sized and high-density LFP energy-type lithium iron phosphate to meet the needs of new energy vehicles, especially buses and special-purpose vehicles.
Nickel-cobalt-manganese and nickel-cobalt-aluminum ternary materials are currently promising cathode materials. They make good use of the advantages of lithium manganese oxide, lithium cobalt oxide, and lithium nickel oxide, while making up for the shortcomings of each material to a certain extent. Ternary materials have relatively balanced performance, high energy density and capacity (capacity can reach 180-190 mAh/g), good cycle performance (up to 2000 cycles), strong endurance, and relatively low price. However, they have poor safety and low-temperature performance, are difficult to synthesize, and have low charge and discharge efficiency.
2. Research and development of cathode materials
The research and development of nickel-cobalt-manganese and nickel-cobalt-aluminum ternary materials mainly focuses on improving the volumetric energy density, enhancing low-temperature performance, and improving battery safety; performance is regulated by adjusting the composition ratio of the materials. To further improve battery energy density, cathode materials will develop towards silicate composites, layered lithium-rich manganese-based materials, and sulfur-based materials; and towards materials with higher lithium insertion/extraction capacity and good reversible lithium insertion/extraction performance. Material structure research tends towards layered and spinel structures.
3. Development Trends of Cathode Materials
(1) Material modification
The stability of the surface structure of the electrode material is mainly achieved through graphene modification and surface modification, which can improve the material's conductivity, high-temperature cycling performance, and reduce capacity decay.
(2) Ion doping
Ion doping mainly involves doping transition metals and non-metals with metallic elements such as aluminum (Al), chromium (Cr), and magnesium (Mg) at oxygen sites. This process incorporates highly conductive metal ions into cathode materials, improving lithium-ion diffusion rate, conductivity, electrochemical performance, and stability. Further research is needed to understand the specific mechanisms of doping modification in order to better utilize doping to enhance material performance.
(3) Material nanofiber
By reducing the particle size of the cathode material, the diffusion path is shortened, the diffusion rate is increased, and the specific surface area of the material is increased, more diffusion channels are added, the reaction is accelerated, the insertion/extraction rate and specific power of the cathode material are improved, and the electrochemical activity is enhanced.
(4) Composite cathode materials
As the requirements for lithium-ion power batteries continue to increase, the trend of selecting complementary cathode materials for composites is becoming increasingly apparent, such as sulfur/graphene composite cathode materials. The key point is how to fully leverage the performance advantages of various composite materials.
II. Lithium-ion battery anode materials
Lithium-ion battery anode materials should possess high conductivity, the ability to accommodate a large number of lithium ions, and good stability. Currently, most anode materials are graphite-structured carbon materials, typically made by mixing carbon materials, binders, and additives in a certain proportion, coating them onto copper foil, and then drying and rolling them. Other materials include silicon-based materials, tin-based materials, and lithium titanate materials. Major domestic manufacturers of lithium-ion battery anode materials include Shenzhen Berryt Technology Co., Ltd., Shanghai Shanshan Technology Co., Ltd., Jiangxi Zichen Technology Co., Ltd., Shenzhen Snow Industrial Development Co., Ltd., Hunan Xingyuan Technology Development Co., Ltd., and Jiangxi Zhengtuo New Energy Technology Co., Ltd.
1. Main anode materials
The main anode materials for lithium-ion batteries are graphite-based materials, including artificial graphite, natural graphite, soft/hard carbon and mesophase carbon microspheres, and lithium titanate; anode materials under research include titanium oxide, tin-carbon composites, silicon composites, carbon nanotubes, and novel graphite materials.
Natural graphite is abundant and inexpensive, and its layered structure allows for reversible lithium-ion insertion and extraction. Artificial graphite has mature preparation technology, and the porous structure formed by the random arrangement of secondary particles during preparation facilitates electrolyte penetration and lithium-ion diffusion, improving battery charge/discharge capacity and cycle performance, thus holding a significant advantage in current anode production. Mesophase carbon microspheres are spherical layered particles with good cycle performance and high electrode density, but lower capacity and higher manufacturing costs. Soft carbon materials, while having high capacity values, suffer from rapid degradation, hindering practical applications. Hard carbon materials are easier to prepare, have higher cycle life, and have already achieved some practical applications.
Lithium titanate anode materials have high power characteristics, good safety, good structural stability, fast charge and discharge capability, good cycle performance, and excellent high and low temperature performance. During the lithium ion insertion or extraction process, the volume of the material hardly changes and does not react with the electrolyte, exhibiting high safety. It is very likely to become the main development direction of the next generation of lithium-ion power battery anode materials; however, it has high cost, low energy density and conductivity, and the process technology is not mature.
Carbon-silicon composite materials can effectively improve the cycle performance of silicon anodes and alleviate electrode volume expansion during cycling. Vanadium oxide anode materials have high energy efficiency, excellent cycle performance, and low capacity decay. Transition metal oxide anodes have attracted increasing attention due to their high theoretical capacity, but the generation of low-density lithium oxide during discharge causes electrode volume expansion, leading to battery capacity decay. Iron(III) oxide (Fe3O4) has attracted widespread attention among transition metal oxide anode materials due to its good conductivity and cycle stability. It boasts high theoretical capacity, abundant resources, and is safe and non-toxic. Li3V2(PO4)3 anode materials exhibit excellent capacity stability and low-temperature performance.
2. Research and development of anode materials
Currently, research on anode materials mainly focuses on intercalation, alloying, and conversion types; the main research materials include hard carbon, soft carbon, and silicon-carbon; and efforts are being made to improve process maturity, stability, and efficiency. Currently, the most researched anode materials include nanoscale silicon and silicon alloys (primarily to address the problem of rapid capacity decay caused by large volume changes in silicon anode materials), metal oxides (iron oxide, titanium oxide) to replace graphite, and improving conductivity by coating or controlling the particle size and morphology of the materials. Alloy research mainly focuses on the nano-sizing and multi-component composite of materials. Carbon nanotubes and graphite, novel anode materials, are under research and will bring new opportunities and challenges to the development of lithium-ion batteries.
3. Development Trends of Anode Materials
(1) Optimization of graphite anode
Ion doping can effectively improve the power characteristics and cycle stability of materials, while coating treatment can effectively inhibit particle growth and improve electronic conductivity, resulting in good electrochemical performance.
(2) Material nanofiberization
Carbon nanotubes and graphene are prime examples. Their dispersed spherical nanostructures have a high specific surface area, which can significantly improve the specific capacity, cycle performance, and rate performance of materials.
(3) New type
In order to continuously improve the energy density of lithium-ion power batteries, the future development focus of anode materials will shift to new carbon active materials, alloy materials, and silicon-carbon composite materials; and to improve lithium intercalation capacity.
III. Lithium-ion battery electrolyte materials
Electrolyte, which transports ions and conducts current between the positive and negative terminals of a battery, is one of the key factors for achieving high energy, long lifespan, and safety, and must possess excellent stability. Major manufacturers include Zhangjiagang Guotai Huarong Chemical New Materials Co., Ltd., Shenzhen Xinzhoubang Technology Co., Ltd., Tianjin Jinniu Power Materials Co., Ltd., Guangzhou Tinci Advanced Materials Co., Ltd., and Saiwei (Shenzhen) Electronics Co., Ltd.
1. Main electrolyte materials
The electrolyte in a lithium-ion battery participates in all reactions that occur inside the battery. Overcharging, over-discharging, short-circuiting, or thermal shock can cause the battery temperature to rise, the electrolyte to burn, and the battery to catch fire or even explode. Therefore, the safety of the electrolyte is crucial. It is mainly a solution in which lithium salts are dissolved by organic solvents. The main lithium salts are lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6). The organic solvents are usually carbonates, mainly dimethyl phosphate, methyl ethyl carbonate, ethylene carbonate, and methyl ethyl carbonate; there are also sulfonates, borates, cyclic ethers, polyethers, as well as sulfones, nitriles, and nitro compounds. To maintain the conductivity of the electrolyte, lithium salts are readily soluble in organic solvents and have good thermal stability, but each has its limitations. LiPF6 has poor stability at high temperatures, LiBF4 has low ionic conductivity at room temperature, and LiClO4 has strong oxidizing properties.
2. Research and development of electrolyte materials
Research on novel lithium salts mainly focuses on lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(imine) (LiFSI).
3. Development Trends of Electrolyte Materials
(1) Solidification
To prevent safety issues such as leakage, combustion, and explosion of lithium-ion battery electrolytes, electrolyte materials are being developed towards solid-state materials. The main research directions include inorganic solid electrolytes, solid polymer electrolytes, and solid-liquid composite electrolytes.
(2) Novel solvent system
Nitrile and sulfone solvents are less compatible with graphite anodes than commonly used carbonate solvents. Current research focuses on reducing the cost of novel solvent systems and improving their compatibility with existing anode materials.
(3) High voltage electrolyte
The main research direction for high-voltage electrolytes is to simultaneously improve the voltage levels of the cathode material and the electrolyte.
IV. Lithium-ion battery separator materials
The separator accounts for approximately 20% of the battery cost and is a crucial component of battery materials. Its main function is to isolate the positive and negative electrodes, ensuring battery safety and enabling charging and discharging. High insulation is a primary requirement. As a high-polymer functional material, the separator has broad development prospects, high added value, low cost, and considerable economic benefits. Major domestic separator manufacturers include Xingyuan Electronics Technology (Shenzhen) Co., Ltd., Beijing Taihe Zhongke Technology Co., Ltd., Foshan Jinhui Gaoke Optoelectronic Materials Co., Ltd., Chongqing Mingzhu Plastics Co., Ltd., Henan Yiteng New Energy Technology Co., Ltd., and Nantong Tianfeng Electronic New Materials Co., Ltd.
1. Main membrane materials
To facilitate gas diffusion, thin and highly permeable lithium-ion battery separator materials should be selected, typically polyolefin-based microporous films, including polyethylene monolayers, polypropylene monolayers, and two- or three-layer composite films of these materials, with a film thickness of approximately 10–20 μm. Research on separators mainly focuses on improving strength, stability, and porosity.
2. Research and development of diaphragm materials
Currently, there is an overcapacity in the low-end separator market, but the high-end separator market still lags behind foreign products in quality, with issues of quality uniformity and stability. The market is in short supply and heavily reliant on imports from a few countries such as Japan and the United States.
3. Development Trends of Membrane Materials
(1) Surface modification treatment
The physical properties of diaphragm materials, such as puncture strength, tensile strength, thermal shrinkage rate, high temperature resistance, and high pressure resistance, can be improved by applying inorganic ceramic coatings or organic coatings to modify and strengthen the surface of the diaphragm material.
(2) Thinning of diaphragm materials
To increase the capacity of lithium-ion batteries, the separator must be made thinner and lighter. Mastering the production technology of thin separators will give us an advantage in future competition. However, this also places higher demands on the production and preparation of separator materials and the level of technology, requiring continuous research and development and breakthroughs.
V. Conclusion
With the continuous development of battery research and industry in Japan, South Korea and the United States, the Chinese government has also successively introduced a series of policies to promote the development of the battery industry. Major lithium-ion power battery manufacturers that have developed rapidly in recent years include CALB (Luoyang) Co., Ltd., BYD Co., Ltd., Tianjin Lishen Battery Co., Ltd., Zhejiang Wanxiang Yineng Power Battery Co., Ltd., Guangyu International Group Co., Ltd., Shenzhen BAK Battery Co., Ltd., Shenzhen Wotema New Energy Vehicle Power Battery Co., Ltd., Hefei Guoxuan High-tech Power Energy Co., Ltd., and CITIC Guoan Mengguli Power Technology Co., Ltd. However, there is still a certain gap with the international advanced level in terms of key materials and overall battery production.
In recent years, to reduce reliance on traditional petrochemical energy and conserve energy to reduce emissions and mitigate the greenhouse effect, the large-scale promotion and application of electric vehicles has become an inevitable trend. Therefore, improving the overall performance of power batteries and reducing costs to within consumers' affordability range have become the main competitive goals for battery manufacturers. With continuous breakthroughs in lithium-ion power battery technology bottlenecks and continuous cost reductions, it is foreseeable that lithium-ion power batteries will become the future direction of battery technology development and a target pursued by more and more automakers.
