High-Nickel Cathode Strain Control for Cycle-Stable Li Batteries
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Solution Overview
Problem
Lithium secondary batteries face challenges in achieving high energy density and stability, particularly due to the instability and capacity retention issues associated with lithium metal oxides when increasing energy density and output.
Innovation Solution
A cathode for lithium secondary batteries is designed with a lithium metal oxide containing a specific nickel content and strain value, calculated using XRD analysis, to maintain structural stability and prevent lattice structure collapse during charging and discharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the energy density and capacity of lithium metal oxide are increased, then the energy density and output of the battery are improved, but the stability and capacity retention rate of the lithium metal oxide are reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the nickel content (x ≥ 0.80) and lithium content (a ≥ 0.95) in the lithium metal oxide compound LiₐNiₓMᵦO₂, and by controlling the lattice strain Q to satisfy the relationship Q < 11.5x - 7.9. This parameter optimization resolves the contradiction by achieving high energy density through high nickel content while maintaining stability through controlled lattice strain, thereby improving both energy density and capacity retention rate simultaneously
Solution Approach 2:
The patent uses composite materials by incorporating multiple transition metals (nickel, cobalt, manganese) in the lithium metal oxide compound LiₐNiₓMᵦO₂. The composite structure combines the high capacity contribution from nickel with the structural stability provided by cobalt and manganese, resolving the contradiction between high energy density and stability by leveraging the complementary properties of different metal elements
2Power
If the nickel content in lithium metal oxide is increased to improve energy density, then the output capacity is improved, but the lattice structure stability is reduced leading to capacity retention issues
Solution Approach 1:
The patent applies parameter changes by establishing a quantitative relationship between nickel content (x) and lattice strain (Q), where Q < 11.5x - 7.9. This allows high nickel content (x ≥ 0.80) for high output capacity while maintaining lattice stability through controlled strain, resolving the contradiction between power and compositional stability
Solution Approach 2:
The patent applies beforehand cushioning by pre-controlling the lattice strain through specific composition design before battery operation. By designing the lithium metal oxide with predetermined nickel and lithium content ratios that satisfy the strain relationship Q < 11.5x - 7.9, the lattice structure is pre-stabilized to withstand the stresses of high-capacity operation, preventing capacity retention degradation
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 cathode provides improved energy density, capacity, and stability by controlling lattice strains within a predetermined range, enhancing operational stability and reducing gas generation, thereby improving cycle life characteristics.
Implementation Method 1
Each of the lattice strains may be 1/4 of the slope of a straight line obtained by plotting a diffraction angle θ (rad) and a full width at half maximum β (rad) of XRD peaks of the lithium metal oxide, obtained by XRD analysis at each measurement voltage
Implementation Method 2
Q may represent the maximum value among lattice strains measured according to voltage within a voltage range of 3.0 V to 4.3 V
Data Source
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Figure 5
AI summary
A cathode for a lithium secondary battery according to exemplary embodiments includes a lithium metal oxide containing nickel and having a strain (Q) that satisfies a predetermined relationship. The strain is a maximum value among lattice strains measured within a predetermined voltage range, and the lattice strains may be calculated from an XRD profile of the cathode. The present disclosure may provide a cathode exhibiting improved structural stability, high-temperature stability and cycle characteristics, as well as enhanced high-capacity and high-power characteristics.