Core-Shell Lithium Battery Cathode for Low-Temperature Resistance
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Solution Overview
Problem
Lithium secondary batteries for automobiles face challenges in maintaining high Li ion conductivity and reducing internal resistance at low temperatures, which affects their cycle life and safety, especially when the Ni composition ratio is high or when using transition metals with different ionic radii.
Innovation Solution
A layered positive electrode material with a composition of LiaMnxNiyCozO2, where 0<a≦1.2, 0.1≦x≦0.9, 0≦y≦0.44, 0.1≦z≦0.6, and x+y+z=1, is developed, with Ni substitution by Mn and Co, and further substitution by elements like Al, B, Fe, Cu, Mg, Zn, Ga, and Si, to control the mixing of transition metals into the lithium layer, optimizing the crystal structure and specific surface area for improved Li ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high Ni composition ratio is used in the positive electrode material, then battery capacity density is improved, but cycle life becomes insufficient and internal resistance increases at low temperature
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the central core region contains high Ni composition (0.35≤x≤0.55) for high capacity, while the outer shell region contains lower Ni composition (0.15≤x≤0.35) for structural stability. This spatial differentiation of composition allows simultaneous achievement of high capacity density and long cycle life, resolving the contradiction between quantity of substance and reliability.
2Quantity of substance
If high Ni composition ratio is used in the positive electrode material, then battery capacity density is improved, but internal resistance at low temperature increases
Solution Approach 1:
The patent creates a compositional gradient where the outer shell has lower Ni content (0.15≤x≤0.35) which maintains lower internal resistance and better low-temperature performance, while the inner core has higher Ni content (0.35≤x≤0.55) for high capacity. This local differentiation resolves the contradiction between capacity density and low-temperature resistance.
Solution Approach 2:
The patent uses composite material strategy by combining two different LiNi1-xMnxO2 compositions to form a core-shell structured composite. The outer shell layer with lower Ni content provides good ionic conductivity at low temperature, while the inner core layer with higher Ni content provides high capacity, achieving both high capacity density and low internal resistance at low temperature.
3Duration of action of stationary object
If transition metal substitution is performed to improve cycling characteristics, then cycle life is improved, but Li ion conductivity at low temperature decreases
Solution Approach 1:
The patent applies local quality by controlling the Mn substitution ratio x to be different in core and shell regions. The shell region has lower substitution ratio (0.15≤x≤0.35) preserving Li ion conductivity pathways, while the core region has higher substitution ratio (0.35≤x≤0.55) enhancing structural stability for long cycle life. This spatial variation resolves the contradiction between cycle life and low-temperature ionic conductivity.
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 approach results in a lithium secondary battery with superior cycle life, safety, and reduced internal resistance at low temperatures, enabling efficient charge and discharge cycles and enhanced thermal stability, suitable for hybrid and electric vehicles.
Implementation Method 1
layered lithium transition metal complex oxide, which is a positive electrode material, has a hexagonal crystal structure, and the crystal structure has a great influence on lithium ion insertion and extraction
Implementation Method 2
when the X-ray diffraction is carried out for the positive electrode material, the diffraction peak of a (003) plane is characteristic of a layered rock-salt structure
Data Source
AI summary
A positive electrode material for a nonaqueous lithium secondary battery and a lithium secondary battery that has superior cycle life and safety and reduced internal resistance of the battery at low temperature is provided. The positive electrode material for a nonaqueous lithium secondary battery comprise a layered structured complex oxide expressed by a composition formula LiaMnxNiyCozMαO2, where 0<a≦1.2, 0.1≦x≦0.9, 0≦y≦0.44, 0.1≦z≦0.6, 0.01≦α≦0.1, and x+y+z+α=1. A diffraction peak intensity ratio between the (003) plane and the (104) plane (I(003)/I(104)) in an X-ray powder diffractometry using a Cu—Kα line in the X-ray source is not less than 1.0 and not more than 1.5.