Lithium-Ion Battery Positive Electrode Coating for Oxidation Resistance
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Solution Overview
Problem
Lithium ion secondary batteries face challenges in achieving excellent charge/discharge rate characteristics and preventing oxidative decomposition of the electrolytic solution when using aqueous binders, as they tend to decompose during charging, leading to degraded performance and gas generation.
Innovation Solution
A positive electrode combination material is developed, comprising a spinel-type lithium-nickel-manganese oxide active material, a non-graphitizable carbon conduction aid, and an aqueous binder with a carboxyl group, such as carboxymethyl cellulose or polyacrylic acid, which provides a balanced surface area ratio to inhibit oxidative decomposition and enhance coating effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an aqueous binder is used in the positive electrode, then oxidation resistance and stability are improved, but oxidative decomposition occurs during charging leading to gas generation and degraded performance
Solution Approach 1:
A coating layer comprising a compound represented by formula (1) is applied to the surface of the positive electrode active material particles. This coating layer acts as an intermediary between the aqueous binder and the high-potential active material, preventing direct contact and oxidative decomposition while allowing lithium ion diffusion, thereby eliminating gas generation while maintaining oxidation resistance
Solution Approach 2:
The positive electrode combines multiple materials with complementary properties: spinel-type lithium-nickel-manganese oxide (LMX) as the active material providing high potential and capacity, aqueous binder (carboxymethyl cellulose or polyacrylic acid) providing oxidation resistance and flexibility, and a coating layer compound providing chemical stability. This composite structure achieves both oxidation resistance and prevention of binder decomposition
2Reliability
If the surface of the positive electrode active material is coated with compound Formula 1, then oxidative decomposition is prevented, but charge/discharge rate characteristics are degraded due to blocked lithium ion movement
Solution Approach 1:
The coating layer's composition parameters are precisely controlled: the compound follows formula (1) with specific ratios where 0 < x ≤ 0.5 and 0 < y ≤ 0.5, and the coating amount is controlled at 1-50 wt% relative to active material. These parameter optimizations ensure the coating is thin enough to allow lithium ion diffusion while thick enough to provide oxidation protection
Solution Approach 2:
The coating layer is designed with porous structure characteristics that allow lithium ions to diffuse through while providing oxidation protection. The porous nature of the coating enables ion transport pathways while maintaining the protective barrier function against oxidative decomposition
3Reliability
If alginate binder is used for excellent oxidation resistance, then stability is improved, but oxidative decomposition occurs at contact points with high-potential active material leading to gas generation
Solution Approach 1:
The coating layer serves as a protective intermediary between the alginate binder and the high-potential LMX active material. This intermediate barrier prevents direct oxidative decomposition at contact points while allowing the binder to maintain its excellent oxidation resistance and flexibility properties
Solution Approach 2:
The coating layer is selectively applied to specific locations where the binder contacts the high-potential active material, providing localized protection at vulnerable contact points while maintaining the overall binder structure and its oxidation resistance properties
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
This configuration achieves improved charge/discharge rate characteristics and suppresses oxidative decomposition, reducing gas generation and maintaining high energy density and operating voltage.
Implementation Method 1
the aqueous binder having a carboxyl group has a high affinity for the surfaces of the positive electrode active material and carbon-based conduction aid, and thus achieves a greater coating effect
Implementation Method 2
smooth movement of lithium ions between the active material and an electrolytic solution
Data Source
AI summary
A positive electrode for a lithium ion secondary battery that includes a positive electrode combination material having a positive electrode active material that produces a potential of 4.5 V or higher on the basis of metal lithium; a conduction aid; and a binder. The binder contains an aqueous binder as its main constituent, and the sum SE of the surface area SA of the positive electrode active material in the positive electrode combination material and the surface area SC of the conduction aid therein is 90 to 400 cm2/cm2 per unit coated area of the positive electrode combination material.