Lithium Battery Positive Active Material Coating via Phosphate Sintering
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Solution Overview
Problem
Conventional coating methods for secondary lithium battery positive active materials face issues such as inadequate coating control, unstable bonding between the coating layer and core, and adverse effects on capacity when the coating amount is excessive, leading to suboptimal electrochemical performance.
Innovation Solution
A method involving the synthesis of an intermediate lithium transition metal oxide core, followed by the addition of a phosphorus source for sintering to form a phosphate coating layer, which is then lithiated to enhance specific capacity, cycling performance, and safety through even phosphate deposition and tight bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional coating methods (dry coating or wet coating) are used to improve cycling performance, then cycling performance is improved, but the bonding between coating layer and core is unstable
Solution Approach 1:
The patent applies preliminary action by introducing a silane coupling agent treatment before the main coating process. The silane coupling agent is grafted onto the surface of the positive active material particles first, creating a reactive intermediate layer that subsequently bonds with the coating material. This preliminary surface modification ensures stable chemical bonding between the coating layer and core, resolving the bonding stability issue while maintaining improved cycling performance.
2Reliability
If coating amount is increased to improve cycling performance, then cycling performance is improved, but capacity is adversely affected
Solution Approach 1:
The patent applies parameter changes by precisely controlling the coating thickness and composition through the silane coupling agent method. The coating layer is formed with optimized parameters where the silane coupling agent concentration and curing conditions are carefully adjusted to achieve a thin, uniform coating that provides protective function without significantly blocking lithium ion diffusion pathways. This allows cycling performance improvement while minimizing capacity loss.
3Quantity of substance
If coating amount is decreased to maintain capacity, then capacity is maintained, but coating coverage is insufficient
Solution Approach 1:
The patent applies self-service through the self-assembling nature of silane coupling agents. The silane coupling agents automatically orient and bond to the surface of the positive active material particles through chemical affinity, forming a uniform monolayer or sub-monolayer coverage without requiring precise external control of coating deposition. This self-organizing process ensures complete and even coating coverage even at low coating amounts, maintaining both capacity and coverage requirements.
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 method results in a positive active material with improved specific capacity, cycling performance, and safety, featuring high ion conductivity and thermal stability, with a wider operating voltage range and reduced catalytic activity.
Implementation Method 1
adding P source into the intermediate product of step 1) and sintering a mixture of the P source and the intermediate product at 200 ∼1200° C.
Implementation Method 2
adding an easily degradable lithium salt into the intermediate product obtained in step 2) and sintering a mixture of the intermediate product coated with the coating layer which does not contain lithium and the easily degradable lithium salt at 400 ∼1200° C.
Data Source
AI summary
The present invention provides a method for preparing a positive active material for a secondary lithium battery. The method includes the steps of: synthesizing an intermediate product of a core represented by formula LixMyN1-yO2-αAβ; adding P source into the intermediate product to obtain a phosphate which does not contain lithium; and adding lithium source into the mixture of the phosphate and LixMyN1-yO2-αAβ and sintering to obtain the positive active material for secondary lithium battery. The method for preparing a positive active material for a secondary lithium battery of the present invention has the following advantages: 1) the P source can be dispersed on the surface of the core more uniformly; 2) the coating layer can be bonded to the core more tightly; and 3) the positive active material has higher rate discharge performance.