Cathode Active Material Surface Control for Low-Residual Lithium
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing cathode active materials for secondary batteries face issues with residual lithium on the surface causing gelation and gas generation, leading to stability and efficiency degradation, while attempts to remove it risk losing internal lithium and altering the electrochemical properties.
Innovation Solution
Control the residual lithium content on the particle surface to be 1 wt% or less and maintain a BET of 0.4 m²/g or more, setting specific organic correlations to ensure optimal electrochemical properties by balancing surface exposure and internal lithium retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If residual lithium is removed through washing process, then gelation and gas generation are suppressed, but internal lithium ions may be removed causing structural changes and degraded electrochemical properties
Solution Approach 1:
The patent applies local quality by treating only the surface region of the cathode active material particles with a coating agent. The coating layer is formed exclusively on the particle surface where residual lithium exists, without penetrating into the internal crystal structure. This selective surface treatment removes residual lithium through reaction with the coating agent while preserving the internal lithium ions and crystal structure integrity, thus suppressing gelation and gas generation without degrading electrochemical properties.
Solution Approach 2:
The patent uses a coating agent as an intermediary substance that reacts with residual lithium on the particle surface. The coating agent serves as a mediator that selectively binds and removes residual lithium without affecting internal lithium ions. By introducing this intermediary coating layer, the harmful residual lithium is eliminated while the beneficial internal lithium is protected, resolving the contradiction between removing surface contaminants and preserving internal structure.
2Stability of the object's composition
If excess Li source is added to form high crystallinity layered structure, then crystallinity is improved, but residual lithium is formed on the surface causing alkalinity and gelation
Solution Approach 1:
The patent applies the extraction principle by removing residual lithium from the particle surface through chemical reaction with a coating agent. The coating agent selectively reacts with and extracts residual lithium (in the form of LiOH, Li2CO3, or other lithium compounds) from the surface, separating it from the desired high-crystallinity layered structure. This allows the material to maintain high crystallinity from excess Li source addition while eliminating the harmful residual lithium that causes alkalinity and gelation.
3Object-generated harmful factors
If residual lithium is reduced on particle surface, then gelation is suppressed, but BET increases due to exposed curved surface
Solution Approach 1:
The patent applies parameter changes by controlling the residual lithium content within a specific range (0.1-5 wt%) rather than completely eliminating it. By maintaining residual lithium within this optimized parameter range and applying surface coating treatment, the patent achieves a balance where sufficient residual lithium remains to maintain surface properties and limit BET increase, while enough is removed to suppress gelation. This parameter optimization resolves the contradiction between suppressing gelation and controlling BET increase.
Data Source
AI summary
The present invention provides a cathode active material for secondary batteries, which comprises a transition metal, has a residual lithium content on the particle surface of 1 wt% or less, and a BET surface area of 0.4 m2/g or more.