High-Ni Cathode Material Coating for Cycle Stability
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Solution Overview
Problem
Existing non-aqueous electrolyte secondary batteries with high Ni content in the positive electrode active material face instability in the layered structure, leading to decreased battery capacity with repeated charge/discharge cycles.
Innovation Solution
A positive electrode active material is developed with a lithium transition metal composite oxide containing Ni at 80 mol% or more, coated with a surface modification layer comprising Sr, Ca, or Ba, which stabilizes the structure and enhances output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the Ni content is increased to 80 mol% or more to obtain high discharge capacity, then the battery capacity is improved, but the layered structure becomes unstable and battery capacity decreases with repeated charge/discharge cycles
Solution Approach 1:
A surface modification layer containing Sr, Ca, and Ba is introduced as an intermediary between the high-Ni lithium transition metal composite oxide and the electrolyte. This surface layer stabilizes the crystal structure by suppressing cation mixing and preventing structural degradation during charge/discharge cycles, while allowing the high Ni content (80 mol% or more) to maintain high discharge capacity.
Solution Approach 2:
The positive electrode active material is designed as a composite structure combining lithium transition metal composite oxide with high Ni content (80 mol% or more) and a surface modification layer containing Sr, Ca, and Ba. This composite approach enables the core material to provide high capacity while the surface layer provides structural stability, resolving the contradiction between capacity and stability.
2Quantity of substance
If the Ni content is increased to 80 mol% or more to obtain high discharge capacity, then the battery capacity is improved, but the charge/discharge cycle characteristics deteriorate
Solution Approach 1:
The surface modification layer containing Sr, Ca, and Ba acts as a protective intermediary that prevents direct contact between the high-Ni active material and the electrolyte. This intermediary layer suppresses harmful surface reactions and structural degradation, thereby improving charge/discharge cycle characteristics while maintaining high discharge capacity through the high Ni content.
Solution Approach 2:
The surface modification layer changes the surface composition parameters by introducing Sr, Ca, and Ba elements. This parameter change creates a more stable surface chemistry that prevents capacity fade during cycling, allowing the bulk material to maintain high Ni content (80 mol% or more) for high discharge capacity without sacrificing cycle life.
3Reliability
If a surface modification layer containing Sr, Ca, and Ba is formed to stabilize the structure, then the charge/discharge cycle characteristics are improved, but the device complexity increases
Solution Approach 1:
The surface modification layer is applied locally only to the surface of the lithium transition metal composite oxide particles, rather than changing the bulk composition. This local quality approach adds minimal complexity by modifying only the outer surface with Sr, Ca, and Ba, while the core material remains simple high-Ni composition (80 mol% or more), thus improving cycle characteristics without significantly increasing overall device complexity.
Solution Approach 2:
The surface modification layer introduces specific compositional parameters (Sr, Ca, Ba content) at the surface while maintaining the simple high-Ni bulk composition. This parameter differentiation between surface and bulk creates a straightforward two-zone structure that improves cycle characteristics without requiring complex multi-element bulk compositions or complicated processing steps.
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 proposed solution stabilizes the battery structure, improving charge/discharge cycle characteristics and output performance by suppressing reactions with the electrolyte.
Implementation Method 1
a surface modification layer formed on the surface of the primary particles of the lithium transition metal composite oxide, wherein: the lithium transition metal composite oxide at least contains Ni in an amount of 80 mol % or more relative to the total number of moles of metal elements excluding Li, and Al; and the surface modification layer at least contains at least one of Sr or Ca, and Ba
Implementation Method 2
The proposed solution stabilizes the battery structure, improving charge/discharge cycle characteristics and output performance by suppressing reactions with the electrolyte
Implementation Method 3
charging/discharging is performed by causing lithium ions or the like to move between the positive electrode and the negative electrode
Data Source
AI summary
This positive electrode active material for nonaqueous electrolyte secondary batteries contains: a lithium transition metal composite oxide having secondary particles, each of which is formed of aggregated primary particles; and a surface modification layer which is formed on the surface of each primary particle of the lithium transition metal composite oxide. The lithium transition metal composite oxide contains at least Al and 80% by mole or more of Ni relative to the total number of moles of the metal elements excluding Li; and the surface modification layer contains at least Ba, and at least one of Sr and Ca.