Lithium Ion Battery NCM Coating Graphite Optimization
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving both long cycle life and high energy density due to the expansion of positive active materials damaging the interface with the anode, leading to reduced cycle life compared to lithium ion phosphate batteries.
Innovation Solution
A lithium ion secondary battery is developed using a cathode with a positive active material of LixNiaCobMcO2 and an anode with graphite of specific graphitization degree and particle size, which enhances the elastic structure and adhesion, preventing interface damage and maintaining high energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If NCM positive active material is used to achieve high energy density, then the energy density is improved, but the cycle life deteriorates due to volume expansion damaging the anode-cathode interface
Solution Approach 1:
A coating layer comprising at least one of Li2SiO3, Li3PO4, Li2SiO2PO3, Li4SiO4, and Li4SiO4 is formed on the surface of the NCM positive active material particles. This coating layer acts as an intermediary protective barrier between the NCM material and the electrolyte, preventing harmful interactions while allowing lithium ion diffusion. The coating maintains the structural integrity of NCM during charging cycles, preventing volume expansion damage to the interface and thereby extending cycle life while preserving high energy density.
Solution Approach 2:
The patent modifies the surface properties of NCM particles by introducing a protective coating layer with specific chemical composition (Li2SiO3, Li3PO4, etc.). This parameter change in surface chemistry protects the bulk NCM material from degradation while maintaining its high capacity characteristics. The coating layer parameters are optimized to balance protection functionality with lithium ion conductivity.
2Reliability
If graphite with high graphitization degree is used to improve adhesion and elastic structure, then the cycle life is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent specifies precise parameter ranges for graphite negative active material: graphitization degree of 95-99% and average particle size of 3-10 μm. By optimizing these parameters, the graphite achieves enhanced adhesion and elastic structure that accommodates volume changes during cycling, improving cycle life. The controlled particle size distribution also facilitates uniform coating and assembly processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The battery achieves both long cycle life and high energy density by using the specified positive and negative active materials, improving cycle performance without sacrificing energy density.
Implementation Method 1
the volume of NCM will expand when it charges; the expansion force will damage the interface between anode and cathode
Implementation Method 2
graphite having a graphitization degree of 92% to 98% and an average particle size D50 of 6 μm to 18 μm as negative active material
Data Source
AI summary
The present application relates to a lithium ion secondary battery comprising a cathode, an anode, a separator and an electrolyte; wherein the cathode comprises a positive current collector and a positive material layer, wherein the positive material layer comprises a positive active material with a formula LixNiaCobMcO2, M is at least one selected from Mn and Al, 0.95x1.2, 0<a<1, 0<b<1, 0<c<1 and a+b+c=1; wherein the anode comprises a negative current collector and a negative material layer, wherein the negative material layer comprises graphite having a graphitization degree of 92% to 98% and an average particle size D50 of 6 μm to 18 μm as negative active material. The lithium ion secondary battery has long cycle life and high energy density.