Lithium Cobalt Oxide Composite with Island Coating for High Voltage Stability
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Solution Overview
Problem
Lithium cobalt oxide-based positive active materials in lithium secondary batteries suffer from structural instability and capacity reduction due to corrosion by HF at high temperatures and high voltage environments, leading to cobalt elution and unsatisfactory high voltage characteristics.
Innovation Solution
A composite positive active material is developed, comprising a lithium cobalt-based oxide with a particle coating layer of lithium titanium-based oxide and a surface coating layer with a spinel structure, along with a lithium zirconium-based oxide spaced apart from the surface, which is prepared by mixing lithium cobalt-based oxide, titanium, and zirconium precursors and heat-treating them within specific temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium cobalt oxide is used as a positive active material to achieve high energy density, then capacity and energy density are improved, but structural stability deteriorates due to corrosion by HF at high temperatures and high voltage environments
Solution Approach 1:
The patent applies composite materials by combining lithium cobalt oxide with lithium titanium-based oxide coating layers and lithium zirconium-based oxide particles. This composite structure protects the lithium cobalt oxide from HF corrosion while maintaining high capacity, resolving the contradiction between capacity and structural stability at high temperatures and high voltages.
Solution Approach 2:
The patent applies local quality by creating an island-form particle coating portion with lithium titanium-based oxide on the surface of lithium cobalt oxide particles, rather than uniform coating. This localized coating strategy protects critical surface areas from HF corrosion while preserving the high-capacity properties of the bulk lithium cobalt oxide material.
2Stability of the object's composition
If aluminum is doped into lithium cobalt oxide to prevent structural collapse at high voltage, then structural stability is improved, but high voltage characteristics deteriorate to an unsatisfactory level
Solution Approach 1:
The patent uses composite materials by combining lithium cobalt oxide with lithium titanium-based oxide coating and lithium zirconium-based oxide particles. This composite approach provides structural stability without relying solely on aluminum doping, thereby maintaining satisfactory high voltage characteristics while preventing structural collapse.
Solution Approach 2:
The patent introduces lithium titanium-based oxide and lithium zirconium-based oxide as intermediary materials that mediate between the lithium cobalt oxide and the corrosive environment. These intermediary layers protect the lithium cobalt oxide from HF corrosion and stabilize the structure at high voltage without interfering with electrochemical performance.
3Reliability
If a continuous coating layer is formed on the surface of lithium cobalt oxide to prevent corrosion, then protection against HF corrosion is improved, but electrical conductivity deteriorates due to increased surface resistance
Solution Approach 1:
The patent applies local quality by forming an island-form particle coating portion rather than a continuous coating layer. This localized coating approach provides corrosion protection at critical sites while leaving other surface areas exposed, thereby maintaining electrical conductivity and reducing surface resistance compared to full continuous coating.
Solution Approach 2:
The patent utilizes porous or discontinuous coating structure with island-form distribution of lithium titanium-based oxide. This porous architecture provides sufficient corrosion protection pathways while maintaining electrical contact pathways through the gaps between coating islands, thus balancing protection and conductivity.
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 composite material enhances stability and conductivity, reduces surface phase transitions, and improves high voltage characteristics, resulting in extended lifespan and capacity retention of lithium secondary batteries.
Implementation Method 1
a lithium-deficient cobalt oxide phase having a molar ratio of lithium to cobalt of 0.9 or less may be included in an inner portion of the lithium cobalt-based oxide corresponding to the particle coating portion
Implementation Method 2
heat-treating the first precursor mixture, and mixing the product of primary heat treatment together with a zirconium precursor to obtain a second precursor mixture and heat-treating the second precursor mixture
Data Source
AI summary
Provided are a composite positive active material for a lithium secondary battery, a method of preparing the composite positive active material, and a lithium secondary battery containing a positive electrode including the composite positive active material. The composite positive active material may include a lithium cobalt-based oxide, wherein a particle coating portion may be in an island form on a surface of the lithium cobalt-based oxide, the particle coating portion including a first coating layer containing lithium titanium-based oxide, a lithium-deficient cobalt oxide phase having a molar ratio of lithium to cobalt of 0.9 or less may be included in an inner portion of the lithium cobalt-based oxide corresponding to the particle coating portion, and the composite positive active material may include a first lithium zirconium-based oxide spaced apart from a surface of the lithium cobalt-based oxide.