Overlithiated Layered Oxide Cathode with Ion-Conductive Coating

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Solution Overview

Problem

Overlithiated layered oxide cathode active materials in lithium secondary batteries face issues with decreased discharge capacity, voltage decay, and poor high-rate characteristics due to phase transitions and manganese elution during cycling.

Innovation Solution

A cathode active material with an overlithiated layered oxide structure, represented by Formula rLi2MnO3·(1-r)LiaNixCoyMnzM11−(x+y+z)O2, is developed, incorporating an ion-conductive coating layer containing elements like Ti, Al, or Zr to enhance lithium ion conductivity and structural stability, suppressing phase changes and manganese elution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If overlithiated layered oxide is used as cathode active material, then reversible capacity is improved, but discharge capacity and voltage decay during cycling

Engineering Contradiction:

Improvereversible capacityVSAvoiddischarge capacity and voltage decay during cycling

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies composite materials by combining overlithiated layered oxide with a protective coating layer containing lithium phosphate and/or lithium pyrophosphate. This composite structure maintains the high reversible capacity of the overlithiated layered oxide while the coating layer prevents phase transition and maintains structural stability during cycling, thereby resolving the contradiction between high capacity and cycling reliability.

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If overlithiated layered oxide is used, then energy density is improved, but phase transition from spinel-like to cubic structure occurs

Engineering Contradiction:

Improveenergy densityVSAvoidphase transition from spinel-like to cubic structure

Core Design Contradiction:

Use of energy by moving objectVSStability of the object's composition

Solution Approach 1:

The patent applies preliminary anti-action by pre-forming a protective coating layer of lithium phosphate and/or lithium pyrophosphate on the surface of the overlithiated layered oxide before battery assembly. This coating layer acts as a barrier that prevents the phase transition from spinel-like to cubic structure during subsequent cycling, thereby maintaining compositional stability while preserving the high energy density of the overlithiated layered oxide.

Inventive Principle:

Principle #9Preliminary anti-action

3Quantity of substance

If Mn-rich cathode active material is used, then reversible capacity is improved, but Mn elution from surface occurs

Engineering Contradiction:

Improvereversible capacityVSAvoidMn elution from surface

Core Design Contradiction:

Quantity of substanceVSLoss of substance

Solution Approach 1:

The patent applies the intermediary principle by introducing a coating layer of lithium phosphate and/or lithium pyrophosphate as a mediator between the Mn-rich overlithiated layered oxide and the electrolyte. This intermediate layer prevents direct contact between the electrolyte and the cathode material surface, thereby suppressing Mn elution while allowing lithium ion transport, thus maintaining high reversible capacity without manganese loss.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Ease of manufacture

If conventional Li(NixCoyMnz)O2 is used, then cost is reduced, but rate capability and lifetime characteristics at high temperatures are poor

Engineering Contradiction:

ImprovecostVSAvoidrate capability and lifetime characteristics at high temperatures

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies parameter changes by modifying the surface composition and structure of the cathode material through the formation of a lithium phosphate and/or lithium pyrophosphate coating layer. This changes the surface properties to improve rate capability and thermal stability while maintaining the cost-effective Li(NixCoyMnz)O2 bulk composition, thereby resolving the contradiction between low cost and high reliability under demanding conditions.

Inventive Principle:

Principle #35Parameter changes

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 solution improves lithium ion conductivity, reduces resistance, and extends the battery's lifetime by inhibiting voltage decay and maintaining high-rate performance, thereby enhancing the overall energy storage capabilities of lithium secondary batteries.

Implementation Method 1

improve the lithium ion conductivity of a cathode active material containing overlithiated layered oxide and reduce the resistance thereof

Methodology Applied

Scientific EffectIonic conduction: Conduction (electrical)

Implementation Method 2

suppress the elution of Mn from an Mn-rich cathode active material and the lattice change from a spinel phase to a rock-salt phase

Methodology Applied

Scientific EffectPhysical barrier: Physical Containment

Data Source

PatentUS20220388864A1Lithium secondary battery cathode active material, manufacturing method therefor, and lithium secondary battery comprising same

Publication Date: 2022.12.08 ECOPRO BM CO LTD

AI summary

The present invention comprises: an overlithiated layered oxide represented by chemical formula 1 below; and an ion-conductive coating layer on the overlithiated layered oxide represented by chemical formula 1: [chemical formula 1]rLi2MnO3·(1-r)LiaNixCoyMnzM11−(x+y+z)O2 (in chemical formula 1, 0<r≤0.6, 0<a≤1, 0≤x≤1, 0≤y<1, 0≤z<1, and 0<x+y+z<1, and M1 is at least one selected from among Na, K, Mg, Al, Fe, Cr, Y, Sn, Ti, B, P, Zr, Ru, Nb, W, Ba, Sr, La, Ga, Mg, Gd, Sm, Ca, Ce, Fe, Al, Ta, Mo, Sc, V, Zn, Cu, In, S, B, Ge, Si, and Bi).