Lithium Secondary Battery Cathode Blend for Thermal Stability
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Solution Overview
Problem
Lithium secondary batteries face thermal instability and internal short circuits due to metal release from cathodes at high temperatures, leading to potential ignition, especially when stored fully charged, and lack sufficient lifespan and stability under harsh conditions.
Innovation Solution
A lithium secondary battery design incorporating a cathode with a first lithium metal oxide having a concentration gradient region and a second lithium metal oxide with a single particle structure, enhancing electrical and mechanical reliability, and stability by blending these materials in specific weight ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium transition metal oxide or lithium metal complex oxide is used as cathode active material and stored in fully charged state at high temperature, then energy density is improved, but thermal stability deteriorates due to metal release and separation from cathode
Solution Approach 1:
The cathode active material employs a concentration gradient structure where metal element concentration varies between central and surface portions. This local variation in composition creates different properties at different locations, with the surface having enhanced stability characteristics to prevent metal release while the interior maintains high energy density, thus resolving the contradiction between energy density and thermal stability
Solution Approach 2:
The invention uses a composite cathode active material consisting of lithium transition metal oxide or lithium metal complex oxide with a specific concentration gradient structure. This composite structure combines regions of different metal concentrations to achieve both high energy density and improved thermal stability, preventing the metal release that causes thermal instability in conventional uniform composition materials
2Ease of manufacture
If conventional cathode active material is used, then manufacturing simplicity is maintained, but lifespan and stability under harsh conditions are insufficient
Solution Approach 1:
The invention modifies the compositional parameters of the cathode active material by creating a concentration gradient of metal elements between central and surface portions. This parameter change in metal concentration distribution enhances lifespan and stability under harsh conditions while maintaining compatibility with existing manufacturing processes, thus resolving the contradiction between manufacturing simplicity and reliability
3Object-affected harmful factors
If external shock occurs to battery, then mechanical impact is applied, but internal short circuit and ignition occur due to drastic heat increase
Solution Approach 1:
The concentration gradient structure in the cathode active material acts as a preventive measure against mechanical shock-induced failures. The enhanced stability characteristics at the surface region provide a protective effect that cushions against external shocks, preventing internal short circuits and the subsequent heat generation and ignition risks that would otherwise occur
Data Source
AI summary
A lithium secondary battery comprises a cathode, an anode, a separator and a nonaqueous electrolyte solution. The cathode includes a first cathode active material in which at least one of metals included in the first cathode material has a concentration gradient region between a central portion and a surface portion, and a second cathode active material having a single particle structure. The lithium secondary battery has improved life-span and penetration stability.