Core-Shell LiCoO2 Cathode for High-Voltage Stability
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Solution Overview
Problem
Rechargeable lithium batteries face limitations in energy density, safety, and cycling stability due to the inherent properties of LiCoO2 cathode materials, particularly at higher charge voltages, where increased surface area leads to poor safety and stability, and high cobalt content results in high costs and inferior high-voltage stability.
Innovation Solution
A lithium metal oxide powder with a core-shell structure is developed, where the surface layer has a higher manganese and nickel concentration than the core, and a specific composition gradient is achieved through sintering, allowing for improved lithium diffusion and reduced electrical conductivity, enhancing rate performance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the surface area of LiCoO2 cathode material is increased to improve rate performance, then lithium diffusion is enhanced, but safety and cycling stability deteriorate due to increased side reactions with electrolyte
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core maintains high LiCoO2 content for fast lithium diffusion, while the shell contains enriched Mn and Ni that provide stability and reduce side reactions. This spatial differentiation of composition allows each region to fulfill its specific function optimally.
Solution Approach 2:
The invention creates a composite cathode material combining LiCoO2 with Li-Ni-Mn-Co oxide phases through controlled sintering. The composite structure integrates the high conductivity of LiCoO2 with the stability of Li-Ni-Mn-Co oxide, achieving both fast lithium diffusion and improved safety.
2Use of energy by moving object
If the charging voltage is increased to improve energy density, then energy storage capacity is enhanced, but safety and cycling stability worsen due to severe side reactions and structural degradation
Solution Approach 1:
The patent changes the compositional parameters of the cathode material by controlling the sintering process to create a specific gradient structure with enriched Mn and Ni at the surface. This compositional modification allows the material to withstand higher charging voltages without severe degradation.
Solution Approach 2:
The shell structure with enriched Mn and Ni acts as a protective layer that cushions the core LiCoO2 from severe side reactions at high voltage. This pre-formed protective structure prevents direct exposure of the core to harsh electrolyte conditions during high-voltage operation.
3Use of energy by moving object
If high cobalt content is used in LiCoO2 to achieve high volumetric energy density, then energy storage is improved, but cost increases and high-voltage stability deteriorates
Solution Approach 1:
The patent applies local quality by concentrating Co in the core region where it provides high volumetric energy density, while the shell region is enriched with Mn and Ni that provide high-voltage stability. This spatial separation allows each element to contribute its optimal properties to the overall performance.
Solution Approach 2:
The invention creates a composite structure combining Co-rich LiCoO2 core with Mn-Ni enriched shell phase. This composite approach maintains the high energy density contribution from Co while the Mn-Ni shell provides the necessary high-voltage stability, reducing overall Co content requirements.
4Reliability
If low surface area is used to improve safety and reduce side reactions, then stability is enhanced, but rate performance deteriorates due to limited lithium diffusion pathways
Solution Approach 1:
The patent resolves this contradiction by creating local quality differences within the particle structure. The core maintains properties favorable for stability while the shell provides enhanced lithium diffusion pathways and reaction sites, allowing the particle to exhibit both high stability and fast kinetics.
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 resulting cathode material exhibits improved high-voltage stability, cycling performance, and energy density, with significantly lower electrical conductivity than current cathode materials, enabling efficient lithium-ion battery operation.
Implementation Method 1
The sintering temperature is high enough to allow for an exchange of cations between the LiCoO2 and Li—Ni—Mn—Co oxide phases being formed
Data Source
AI summary
Disclosed are a cathode active material and a method to produce the same at low cost. The cathode powder comprises modified doped LiCoO2 carrying a secondary phase having either one of space groups Fm-3m or Fd-3mS. The modified LiCoO2 is Ni and Mn bearing and has regions of low and high manganese content, where regions with high manganese content are located in islands on the surface. The cathode material has high cycling stability, a very high rate performance and good high temperature storage properties.