Lithium-Excess Cathode Composition for Cycle-Stable Energy Density
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Solution Overview
Problem
Lithium secondary batteries using 'lithium excess type' active materials face challenges in maintaining high energy density and energy density retention rate during charge-discharge cycles, particularly in automotive applications such as electric vehicles.
Innovation Solution
A lithium transition metal composite oxide with an α-NaFeO2 type crystal structure, represented by the formula LiwNi x Co y Mn z O1+w, where w > 1, x + y + z = 1, and specific molar ratios of x, y, and z are adjusted to optimize energy density and retention, achieved through a method involving coprecipitation and firing of transition metal and lithium compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the molar ratio Mn/Me exceeds 0.5 in LiMeO2 type active material, then the discharge capacity increases to 150-180 mAh/g, but the crystal structure changes from α-NaFeO2 type to spinel type during charging, resulting in poor charge-discharge cycle performance
Solution Approach 1:
The patent changes the chemical composition parameters by introducing a lithium excess type active material with formula Li a MeO 1+a where a > 1, and specifically controls the molar ratio of Li to Me to be greater than 1. This parameter change allows the material to maintain the α-NaFeO2 crystal structure even when Mn/Me ratio exceeds 0.5, preventing structural transformation to spinel type during charging while maintaining high discharge capacity
Solution Approach 2:
The patent creates a composite material system by combining multiple transition metals (Ni, Co, Mn) in specific ratios within the lithium excess type structure. The composite oxide Li a Ni x Co y Mn z O 1+a integrates the benefits of different metals: Ni provides high capacity, Co provides stability, and Mn provides cost-effectiveness, while the lithium excess composition maintains structural integrity during cycling
2Reliability
If LiCoO2 is used as the positive active material, then the battery achieves practical use with stable performance, but the discharge capacity is limited to about 120-130 mAh/g
Solution Approach 1:
The patent changes the stoichiometric parameters by using a lithium excess type active material where the molar ratio of Li to Me exceeds 1 (a > 1 in Li a MeO 1+a). This deviation from stoichiometric composition enables the material to achieve discharge capacity of 150-180 mAh/g while maintaining structural stability and charge-discharge cycle performance through the specific composition range defined in the patent
3Quantity of substance
If a lithium excess type active material with Li/Me > 1 and Mn/Me > 0.5 is used, then the α-NaFeO2 structure is maintained after charging with high discharge capacity, but the energy density retention rate decreases during charge-discharge cycles
Solution Approach 1:
The patent optimizes the composition parameters by defining specific ranges for a, x, y, and z in the formula Li a Ni x Co y Mn z O 1+a. The lithium excess ratio (a-1) is controlled to balance capacity and retention, while the transition metal ratios are optimized to maintain structural stability. This parameter optimization achieves both high discharge capacity and improved energy density retention rate during charge-discharge cycles
Solution Approach 2:
The patent uses a composite oxide structure Li a Ni x Co y Mn z O 1+a where multiple transition metals work synergistically. The specific composition ratios are designed to maintain the α-NaFeO2 structure during charging while providing high capacity, and the composite nature of the material improves energy density retention rate by distributing stress and preventing structural degradation during cycling
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 provides a lithium excess type positive active material with high energy density and retention rate, enhancing the performance of lithium secondary batteries in automotive applications by maintaining high energy density and efficiency across charge-discharge cycles.
Implementation Method 1
a method involving coprecipitation and firing of transition metal and lithium compounds
Implementation Method 2
firing the mixture to produce a lithium transition metal composite oxide having an α-NaFeO 2 type crystal structure
Data Source
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AI summary
A positive active material for a lithium secondary battery containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has an α-NaFeO2 type crystal structure, and is represented by formula LiwNixCoyMnzO1+w (w > 1, x + y + z = 1) 0.30 < x < 0.37, 0 ≤ y < 0.05, 0.63 < z < 0.70, and 0.47 < (w - 2x - y)/w < 0.51, or formula LiaNixCoyMnzO1+a (1 < a, x < z, x + y + z = 1), -0.06 ≤ ω ≤ 0.06, ω = 2 - (a - 2x - y)/(z - x), and 0 ≤ y ≤ 0.105.