Nickel-Based Composite Cathode Core-Shell Structure for Lithium Diffusion
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Solution Overview
Problem
Lithium secondary batteries face challenges with high energy density due to increased CO2 gas generation, decreased lithium diffusion rates, and cation mixing caused by excess lithium in positive electrode active materials, leading to structural breakdown.
Innovation Solution
A nickel-based composite positive electrode active material is developed, comprising secondary particles with a core of nickel-based lithium metal oxide in a layered phase and a surface portion with a composite structure of spinel and layered phases, achieved through a method involving primary and secondary heat treatments to control cation mixing and enhance ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If excess lithium is introduced to increase capacity, then battery capacity is improved, but CO2 gas generation increases due to side reactions with electrolyte
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the surface portion has different composition and properties than the core. The surface portion contains reduced excess lithium and modified chemistry to prevent side reactions with electrolyte, while the core maintains high lithium content for capacity. This resolves the contradiction by localizing the harmful excess lithium away from the electrolyte interface.
Solution Approach 2:
The patent uses composite materials by combining multiple phases (layered phase in core, spinel phase in surface portion) with different properties. The composite structure allows the bulk material to provide high capacity while the surface composite layer provides protection against side reactions, thus resolving the contradiction between capacity and CO2 generation.
2Quantity of substance
If excess lithium is introduced to increase capacity, then battery capacity is improved, but lithium diffusion rates decrease due to enlarged particles and cation mixing
Solution Approach 1:
The surface portion with spinel phase provides fast lithium diffusion pathways at the particle surface and interface regions, compensating for the slowed diffusion in the enlarged core particles. This local enhancement of diffusion properties resolves the contradiction between high capacity (requiring large particles) and fast diffusion (requiring small particles).
Solution Approach 2:
The composite of layered and spinel phases creates multiple lithium diffusion pathways. The spinel phase provides three-dimensional diffusion channels that are faster and less prone to cation mixing, while the layered phase provides capacity. This composite structure resolves the diffusion bottleneck in large high-capacity particles.
3Quantity of substance
If excess lithium is introduced to increase capacity, then battery capacity is improved, but positive electrode active material structure breaks down due to cation mixing
Solution Approach 1:
The surface portion is designed with different composition (reduced excess lithium, spinel phase formation) to stabilize the structure at the critical interface region where cation mixing would otherwise occur most readily. This localized structural stabilization prevents overall structure breakdown while maintaining high capacity in the core.
Solution Approach 2:
The patent applies preliminary anti-action by pre-modifying the surface portion before full structure degradation can occur. The controlled formation of spinel phase and reduction of excess lithium at the surface creates a protective layer that prevents cation mixing and structure breakdown from propagating into the bulk material.
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 nickel-based composite active material improves charge and discharge efficiency, ion conductivity, and lifespan by facilitating easier lithium diffusion and reducing cation mixing, thereby enhancing the high-rate properties and capacity of lithium secondary batteries.
Implementation Method 1
performing a primary heat treatment to obtain a first nickel-based active material; and mixing a second nickel-based active material having a molar ratio (Li/Me) of lithium metal (Li) to metals other than Li (Me) of less than 1 with the first nickel-based active material, and performing a secondary heat treatment
Data Source
AI summary
A nickel-based composite positive electrode active material for a lithium secondary battery is in the form of secondary particles each comprised of a plurality of primary particles, each primary particle of the plurality of primary particles having a core portion formed of a nickel-based lithium metal oxide having a layered phase and a surface portion positioned on the core portion, wherein the surface portion has a spinel phase and the layered phase. A method of preparing the nickel-based composite positive electrode active material, and a lithium secondary battery containing a positive electrode including the nickel-based composite positive electrode active material are also provided.