Layered Rock-Salt Cathode Surface Structure for Cycle Stability

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Solution Overview

Problem

Lithium-ion secondary batteries face challenges in maintaining capacity and stability due to deformation and degradation of positive electrode active materials during charge and discharge cycles, leading to reduced cycle performance and safety concerns.

Innovation Solution

A positive electrode active material with distinct inner and outer regions, comprising a non-stoichiometric compound containing titanium and a stoichiometric compound containing magnesium, is coated with a graphene oxide layer to prevent deformation and enhance stability, using a sol-gel method and segregation process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a positive electrode active material is used in lithium-ion secondary batteries, then high energy density and output are achieved, but the material undergoes deformation and degradation during charge and discharge cycles, leading to reduced cycle performance

Engineering Contradiction:

Improveenergy density and outputVSAvoidcycle performance

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The positive electrode active material is divided into an inner region and an outer region with distinct compositions and functions. The inner region contains a non-stoichiometric compound (e.g., Li1+xM1-yO2 where M is a transition metal) that provides high capacity, while the outer region contains a stoichiometric compound that maintains structural stability during cycling, thereby resolving the contradiction between high power and reliability

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent creates a composite structure where the inner non-stoichiometric compound region is combined with an outer stoichiometric compound region. This composite material approach allows the inner region to deliver high energy density while the outer region provides structural integrity and resistance to degradation, simultaneously achieving high power and improved cycle performance

Inventive Principle:

Principle #40Composite materials

2Duration of action of moving object

If the positive electrode active material undergoes repeated charge and discharge cycles, then battery operation is maintained, but capacity reduction and material degradation occur

Engineering Contradiction:

Improvebattery operation continuityVSAvoidcapacity retention

Core Design Contradiction:

Duration of action of moving objectVSReliability

Solution Approach 1:

The outer region of the positive electrode active material is designed to act as a protective buffer that prevents deformation and degradation of the inner high-capacity region during charge and discharge cycles. This beforehand cushioning structure absorbs mechanical stress and prevents capacity reduction, allowing continuous battery operation while maintaining capacity retention

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Quantity of substance

If high-capacity positive electrode materials are used, then energy density increases, but safety concerns arise due to material degradation

Engineering Contradiction:

Improveenergy capacityVSAvoidsafety concerns from degradation

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

Different regions of the positive electrode active material are assigned different compositions and properties: the inner region has non-stoichiometric composition for high capacity, while the outer region has stoichiometric composition for safety and stability. This local quality differentiation allows the material to simultaneously achieve high energy capacity and safety by placing appropriate materials in appropriate locations

Inventive Principle:

Principle #3Local quality

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 structure and coating significantly improve the cycle performance and safety of lithium-ion secondary batteries by preventing material degradation and maintaining capacity, while ensuring high reliability and stability during charging and discharging.

Implementation Method 1

using a sol-gel method and segregation process

Methodology Applied

Scientific EffectSol-gel method: Sol

Implementation Method 2

using a sol-gel method and segregation process

Methodology Applied

Scientific EffectSegregation: Segmentation

Data Source

PatentUS20250273650A1Positive Electrode Active Material, Method for Manufacturing Positive Electrode Active Material, and Secondary Battery

Publication Date: 2025.08.28 SEMICON ENERGY LAB CO LTD

AI summary

A positive electrode active material which can improve cycle characteristics of a secondary battery is provided. Two kinds of regions are provided in a superficial portion of a positive electrode active material such as lithium cobaltate which has a layered rock-salt crystal structure. The inner region is a non-stoichiometric compound containing a transition metal such as titanium, and the outer region is a compound of representative elements such as magnesium oxide. The two kinds of regions each have a rock-salt crystal structure. The inner layered rock-salt crystal structure and the two kinds of regions in the superficial portion are topotaxy; thus, a change of the crystal structure of the positive electrode active material generated by charging and discharging can be effectively suppressed. In addition, since the outer coating layer in contact with an electrolyte solution is the compound of representative elements which is chemically stable, the secondary battery having excellent cycle characteristics can be obtained.