Lithium Iron Cobalt Phosphate Cathode for Thermal Stability
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Solution Overview
Problem
Lithium secondary batteries face challenges in high temperature storage stability and cycle performance, particularly when used in industrial applications where conventional batteries fail to maintain performance and safety due to thermal instability and capacity retention issues.
Innovation Solution
A polyanion-based positive active material represented by the formula LiyFe(1-x)CoxPO4, where 0<x≦0.019, is used in conjunction with a carbon material capable of lithium ion insertion and extraction, forming a solid solution within the olivine structure to enhance high temperature storage stability and cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional lithium-containing transition metal oxides (LiCoO2, LiNiO2, LiMn2O4) are used as positive active materials, then high energy density and good charge-discharge performance are achieved, but thermal instability and safety issues occur at high temperatures
Solution Approach 1:
The patent uses lithium iron phosphate (LiFePO4) with an olivine structure as a composite positive active material. This material combines iron phosphate with lithium to create a structure that maintains high energy density while providing superior thermal stability through the olivine crystal structure, resolving the contradiction between energy density and thermal stability
Solution Approach 2:
The patent changes the chemical composition parameters by using LiFePO4 instead of conventional LiCoO2 or LiNiO2. This parameter change in the active material composition fundamentally alters the thermal properties while maintaining electrochemical performance, allowing the battery to operate safely at high temperatures
2Adaptability or versatility
If conventional batteries are used in high temperature environments, then industrial applications are enabled, but battery life becomes very short due to thermal degradation
Solution Approach 1:
The olivine-structured LiFePO4 composite material provides inherent thermal stability that prevents degradation at high temperatures. The strong covalent bonding in the phosphate groups and the stable olivine structure prevent oxygen release and structural collapse, enabling long battery life in high temperature industrial applications
Solution Approach 2:
The patent creates a chemically inert environment within the battery by using LiFePO4, which does not react with the electrolyte or release oxygen even at elevated temperatures. This inert chemical environment prevents thermal runaway and extends battery life in high temperature conditions
3Use of energy by moving object
If lithium iron phosphate with high theoretical capacity (170 mAh/g) is used, then high energy density is achieved, but capacity retention and cycle performance deteriorate due to structural instability
Solution Approach 1:
The patent uses LiFePO4 with an olivine structure that combines high theoretical capacity with structural stability. The olivine crystal structure provides a stable framework that maintains integrity during lithium insertion and extraction cycles, enabling both high energy density and excellent cycle performance
Solution Approach 2:
The patent optimizes the local structural quality by utilizing the olivine crystal structure with specific FeO6 octahedra arrangements. This local structural arrangement provides stable lithium diffusion pathways while maintaining overall structural integrity, improving capacity retention without sacrificing energy density
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 solution significantly improves high temperature storage stability, capacity retention, and cycle performance of lithium secondary batteries, ensuring long-lasting and high-capacity energy storage suitable for industrial applications.
Implementation Method 1
a carbon material capable of insertion and extraction a lithium ion
Implementation Method 2
the redox reaction generated alone with electrochemical insertion and extraction of lithium in and from LiFePO4 proceeds at a relatively low potential around 3.4 V (vs. Li/Li+)
Data Source
AI summary
The invention provides a polyanion-based positive active material which can improve storage stability (especially, high temperature storage stability), charge and discharge cycle performance and the like of a lithium secondary battery, and a lithium secondary battery using the same. The positive active material for a lithium ion secondary battery contains lithium iron cobalt phosphate represented by the general formula: LiyFe(1-x)CoxPO4(0<x≦0.019, 0≦y≦1.2). By using the positive active material for a lithium secondary battery, high temperature storage stability and charge and discharge cycle performance can be improved in comparison with a case where LiyFePO4 containing no Co is used. By using the positive active material, a lithium ion secondary battery can be suitable for applications in fields of electric automobiles and industrial batteries in which long lives, high capacities, and high output powers are required.