Four core material functional systems of lithium batteries
Positive electrode materials
Functional positioning: lithium ion storage source, accounting for more than 30% of the total battery cost, dominating energy density and working voltage
Mainstream types:
Lithium cobalt oxide (LiCoO₂): energy density of 200Wh/kg, used in mobile phones/laptops, but cobalt resources are scarce and thermal stability is poor
Lithium manganese oxide (LiMn₂O₄): low cost, high safety (150Wh/kg), used in power tools, high temperature environment cycle performance degradation
Ternary materials (LiNiₓCoᵧMn₂O₂): energy density exceeds 250Wh/kg, balances performance and cost, dominates the electric vehicle market, high nickel formula increases the risk of thermal runaway
Lithium iron phosphate (LiFePO₄): extremely high safety, long cycle life (140Wh/kg) , low cost but weak low temperature performance, widely used in commercial vehicles and energy storage power stations
Negative electrode materials
Functional positioning: lithium ion embedding carrier, determines the charge and discharge rate and cycle life
Commercial solutions:
Graphite negative electrode: excellent conductivity, volume change <10%, cycle life >1000 times, theoretical capacity upper limit 372mAh/g restricts energy density improvement
Frontier breakthroughs:
Silicon-based negative electrode: theoretical capacity 4200mAh/g (more than 10 times that of graphite), but the charge and discharge volume expansion of 300% leads to electrode rupture, which needs to be alleviated by nano-silicon-carbon composite (silicon proportion <15%)
Metal tin negative electrode: capacity 992mAh/g, volume expansion 260% leads to a cycle life of less than 200 times
Lithium metal negative electrode: ultimate solution (3860mAh/g), solid electrolyte is required to inhibit dendrite growth
Diaphragm
Functional positioning: electronic insulator and lithium ion selective channel, microporous structure prevents short circuit between positive and negative electrodes
Key technologies:
Porosity of 40%-60% ensures balance between ion conduction and mechanical strength
Porosity of polyethylene (PE) diaphragm is 130℃, blocking current in case of thermal runaway
Ceramic coating improves high temperature resistance to above 200℃
Electrolyte
Functional positioning: ion conductive medium, determines battery safety window and temperature adaptability
System classification:
Liquid electrolyte: lithium hexafluorophosphate (LiPF₆) carbonate solution, used in consumer electronics and power batteries
Gel polymer: polyethylene oxide-bistrifluoromethanesulfonyl imide lithium (PEO-LiTFSI) system, suitable for flexible devices
Solid electrolyte: sulfide/oxide crystal, enabling the next generation of high-safety batteries
New Material research progress
High-capacity positive electrode:
Lithium-rich manganese-based (xLi₂MnO₃·(1-x)LiMO₂) capacity exceeds 300mAh/g
Sulfur positive electrode theoretical energy density 2600Wh/kg, need to overcome the problem of polysulfide dissolution
Fast-charging negative electrode:
Lithium titanate (Li₄Ti₅O₁₂) "zero strain" characteristics achieve 10,000 cycles, but the 1.55V voltage platform reduces the full battery output
Solid electrolyte:
Sulfide (such as Li₁₀GeP₂S₁₂) ion conductivity is close to that of liquid electrolyte, interface impedance and mass production cost hinder industrialization
Material synergy and economy
Positive electrode materials (cost accounting for 30%) dominate energy density, negative electrode materials (15%) determine cycle life, electrolyte (10%) builds a safety window, and diaphragm (20%) undertakes thermal safety protection. The four major materials need to be systematically matched, and the breakthrough of a single material must consider the compatibility of the entire system. The current technology iteration focuses on three major paths: high nickel content in the positive electrode to improve specific energy, silicon-carbon negative electrode to break through the capacity bottleneck, and solid electrolyte to eliminate safety hazards.
