Lithium Cobalt Oxide Core with Discontinuous Surface Layer
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Solution Overview
Problem
Lithium secondary batteries face rapid life decrease due to electrolyte decomposition, active material deterioration, and increased internal resistance, especially at high temperatures, with existing positive electrode active materials like LiCoO2 and LiNiO2 exhibiting low structural stability and poor rate characteristics.
Innovation Solution
A positive electrode active material for lithium secondary batteries is developed, featuring a core of lithium cobalt oxide with a surface modifying layer containing a lithium compound and second lithium cobalt oxide, discontinuously distributed to create a three-dimensional lithium transport path, enhancing lithium ion transport rates and structural stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LiCoO2 is used as the positive electrode active material, then good electrochemical properties and ease of synthesis are achieved, but structural stability is low
Solution Approach 1:
The patent uses a composite material structure with LiCoO2 as the core and Li2SiO3 as the surface coating layer. This composite structure combines the good electrochemical properties of LiCoO2 with the high structural stability of Li2SiO3, resolving the contradiction between ease of synthesis and structural stability.
2Quantity of substance
If LiNiO2 is used to achieve high discharge capacity, then battery properties of high discharge capacity are provided, but thermal stability and cycle property are low
Solution Approach 1:
The patent employs a composite structure where LiCoO2 serves as the core material providing good electrochemical properties, and Li2SiO3 forms a protective surface layer enhancing thermal stability and cycle life. This composite approach achieves high discharge capacity while improving reliability.
3Temperature
If LiMn2O4 is used for low cost and good thermal stability, then cost and thermal stability are improved, but life property is poor due to Jahn-Teller distortion
Solution Approach 1:
The patent uses Li2SiO3 as a surface coating layer on LiCoO2 core. The Li2SiO3 layer prevents Jahn-Teller distortion and structural degradation during cycling, thereby improving life property while maintaining the thermal stability and low cost advantages.
4Volume of stationary object
If active materials with large size are used to increase packing density, then energy per unit volume is increased, but surface area is reduced leading to poor rate characteristic
Solution Approach 1:
The patent applies a surface coating layer of Li2SiO3 on the active material particles. This local modification improves the surface properties and lithium ion transport kinetics at the particle surface, enabling large-sized particles to maintain good rate characteristics while achieving high packing density.
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
This configuration improves the rate characteristic, capacity property, and life of lithium secondary batteries, especially at high temperatures, while maintaining initial capacity and energy density, enabling their use in high-voltage applications.
Implementation Method 1
improving the transport rate of lithium ions via the conversion of the two-dimensional transport path of lithium into a three-dimensional path
Data Source
Figure 1a~1b
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AI summary
The present invention provides a positive electrode active material for a lithium secondary battery including a core including first lithium cobalt oxide, and a surface modifying layer positioned on a surface of the core. The surface modifying layer includes a lithium compound discontinuously distributed on the surface of the core, and second lithium cobalt oxide distributed while making a contact with or adjacent to the lithium compound, with a Li/Co molar ratio of less than 1. The lithium compound includes at least one lithium reactive element selected from the group consisting of Ti, W, Zr, Mn, Mg, P, Ni, Al, Sn, V, Cr, and Mo. The positive electrode active material according to the present invention forms a lithium deficient structure in the positive electrode active material of lithium cobalt oxide and changes two-dimensional lithium transport path into three-dimensional path. The transport rate of lithium ions may increase when applied to a battery, thereby illustrating improved capacity and rate characteristic without decreasing initial capacity. As a result, the positive electrode active material may be useful as a positive electrode active material of a battery for a high voltage with 4.4 V or more.