Core-Shell Lithium Transition Metal Oxide for Battery Rate Performance
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries, particularly those using lithium-excess-type active materials, face challenges in achieving high rate discharge characteristics and cycle performance due to increased resistance in low state of charge regions and insufficient high rate discharge capabilities compared to LiMeO2-type active materials.
Innovation Solution
A lithium-transition metal composite oxide with an α-NaFeO2-type crystal structure is developed, featuring a core-shell structure where the cobalt concentration is higher in the coated part than the core, and the manganese concentration is lower, with a cobalt molar ratio of 3 to 10% in the coated part based on the transition metals in the core, and a cobalt concentration gradient. This composite oxide is synthesized through coprecipitation and firing of transition metal compounds with lithium, optimizing the distribution and concentration of Co, Ni, and Mn.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-excess-type active material is used to achieve high discharge capacity, then discharge capacity is improved, but resistance increases in low SOC region and high rate discharge characteristics deteriorate
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the surface region has different composition (lower Li content, higher transition metal content) compared to the core (higher Li content). This compositional gradient optimizes different regions for different functions: the core provides high capacity while the surface layer improves rate characteristics and reduces resistance in low SOC regions.
Solution Approach 2:
The patent uses composite materials by combining lithium-excess-type lithium transition metal composite oxide with a surface layer having different composition. This composite structure integrates the high capacity advantage of lithium-excess materials with the superior rate characteristics of surface-enriched transition metal regions, resolving the contradiction between capacity and rate performance.
2Quantity of substance
If charge is extended to high potential region (above 4.3 V) to achieve high discharge capacity, then discharge capacity is improved, but cycle performance deteriorates due to increased resistance
Solution Approach 1:
The patent applies preliminary action by pre-forming a protective surface layer with optimized composition before the material undergoes charge-discharge cycling. This surface layer, created during synthesis, preemptively addresses the resistance increase problem that would otherwise occur during cycling at high potentials, thereby maintaining cycle performance while enabling high capacity operation.
Solution Approach 2:
The patent uses local quality by creating a surface region with distinct composition (lower Li content, higher transition metal content) that specifically addresses the high potential charge problem. This localized compositional modification protects the bulk material during high potential charging while maintaining overall high discharge capacity.
3Ease of manufacture
If homogeneous composition is used for simplicity, then manufacturing is simplified, but high rate discharge characteristics and cycle performance are insufficient
Solution Approach 1:
The patent applies parameter changes by systematically varying the composition parameters (Li content, transition metal ratios) across different regions of the material. The compositional gradient, defined by specific ranges of Li content and transition metal ratios in core versus surface regions, creates the necessary performance characteristics while maintaining manufacturability through controlled synthesis parameters.
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 approach results in a nonaqueous electrolyte secondary battery with improved high rate discharge characteristics and cycle performance, enhancing power and discharge capacity retention, particularly when the cobalt concentration gradient and particle size are optimized.
Implementation Method 1
a step of preparing coprecipitation precursor core particles by coprecipitating in an aqueous solution a transition metal compound containing cobalt, nickel and manganese
Implementation Method 2
a step of mixing, with a lithium compound, coprecipitation precursor particles formed by coating the coprecipitation precursor core particles with the compound, and firing the mixture
Data Source
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AI summary
There is provided an active material for a nonaqueous electrolyte secondary battery, including a lithium-transition metal composite oxide which has an α-NaFeO2-type crystal structure and of which the average composition is represented by the composition formula of Li1+αMe1-αO2 (Me is a transition metal containing Co, Ni and Mn; and α > 0), wherein the lithium-transition metal composite oxide is a particle having a core and a coated part, the cobalt concentration of the coated part is higher than the cobalt concentration of the core, the manganese concentration of the coated part is lower than the manganese concentration of the core, and the ratio of cobalt present in the coated part is 3 to 10% in terms of a molar ratio based on the amount of the transition metal present in the core.