Positive Electrode Active Material for Low-SOC Resistance Stability
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Solution Overview
Problem
Nonaqueous electrolyte energy storage devices face challenges in maintaining high power performance at a low state of charge (SOC) after charge-discharge cycles, particularly due to increased resistance from cracking of particles in lithium transition metal composite oxides used as positive active materials.
Innovation Solution
A positive active material comprising a lithium transition metal compound with a polyanion structure, such as LiMPO4, combined with a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, with a specific molar ratio of Mn to Me between 0.4 and 0.6, is used to enhance power performance and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a lithium transition metal composite oxide (NCM) is used as a positive active material, then capacity is improved, but resistance increases due to particle cracking after charge-discharge cycles
Solution Approach 1:
The patent uses a composite material system consisting of NCM particles coated with a lithium transition metal phosphate layer. This composite structure combines the high capacity characteristics of NCM with the stability and low resistance of the phosphate coating, resolving the contradiction between capacity and resistance stability after cycling.
Solution Approach 2:
The patent modifies the surface composition and structure of the NCM particles by coating them with lithium transition metal phosphate. This parameter change at the particle surface level reduces resistance and prevents cracking, thereby maintaining reliability while preserving the bulk capacity of the NCM material.
2Temperature
If a lithium transition metal compound with polyanion structure is used, then thermal stability is improved, but power performance at low SOC deteriorates
Solution Approach 1:
The patent applies local quality by providing different functional characteristics at different locations within the electrode material. The core NCM particles provide high power performance, while the surface-coated lithium transition metal phosphate layer provides thermal stability. This spatial differentiation of properties resolves the contradiction between thermal stability and power performance.
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 combination effectively suppresses the increase in resistance due to particle cracking, maintaining high power performance at low SOC and enhancing thermal stability, even in high-temperature environments, while preventing rapid voltage rises during charge cycles.
Implementation Method 1
a transition metal compound having a polyanion structure forms a polyanion structure by covalently bonding oxygen to an element other than a transition metal, it is known that oxygen is not released even at a relatively high temperature
Implementation Method 2
it is possible to suppress an increase in resistance due to cracking of particles
Data Source
AI summary
A positive active material for a nonaqueous electrolyte energy storage device according to one aspect of the present invention contains a lithium transition metal compound having a polyanion structure and represented by a general formula LiMPO4 (M is one or more elements selected from Fe, Mn, Ni, and Co) or Li3V2(PO4)3, and a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure and represented by a general formula Li1+αMe1−αO2 (0<α, Me is Ni and Mn, or a transition metal element including Ni, Mn, and Co), the lithium transition metal composite oxide having a molar ratio of Mn to the transition metal (Me) of 0.4≤Mn/Me≤0.6.