Negative Electrode Coating for Lithium Battery Cycle Stability

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Solution Overview

Problem

Lithium secondary batteries face issues with increased internal resistance and deteriorated cycle characteristics due to the desorption of boric acid ester compounds from negative electrode active materials during high-rate charge and discharge cycles, leading to reduced battery performance.

Innovation Solution

A negative electrode material with a carbon-based active material and a coating portion containing boron atoms and C—O—C bonding, chemically bonded to the surface, which enhances the stability of the coating layer and prevents desorption, thereby maintaining low internal resistance and cycle performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a boric acid ester compound coating layer is applied on the negative electrode active material surface, then the initial battery performance is improved, but the coating layer gradually desorbs during high-rate charge and discharge cycles, causing internal resistance to increase and cycle characteristics to deteriorate

Engineering Contradiction:

Improvecycle characteristicsVSAvoidcoating layer stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent uses a composite coating structure consisting of a boric acid ester compound layer combined with a silicon oxide layer. This composite structure prevents the desorption of the boric acid ester compound during high-rate charge and discharge cycles while maintaining the initial battery performance benefits, thereby resolving the contradiction between initial performance improvement and coating layer stability.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent modifies the coating layer parameters by controlling the thickness and composition ratio of the silicon oxide layer. By adjusting these parameters, the coating layer maintains its integrity during high-rate cycling, preventing desorption of the boric acid ester compound and maintaining both reliability and compositional stability.

Inventive Principle:

Principle #35Parameter changes

2Power

If the negative electrode active material undergoes repeated expansion and contraction during high-rate charge and discharge, then the battery operates at high power, but the coating layer desorbs from the surface, leading to increased internal resistance

Engineering Contradiction:

Improvecharge and discharge rateVSAvoidinternal resistance increase

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The patent employs a thin film composite coating structure that flexibly accommodates the expansion and contraction of the negative electrode active material during high-rate charge and discharge. The silicon oxide layer acts as a flexible protective shell that prevents the boric acid ester compound from desorbing, thereby maintaining low internal resistance even at high power operation.

Inventive Principle:

Principle #30Flexible shells and thin films

3Duration of action of stationary object

If the coating layer is firmly bonded to the negative electrode active material, then the coating effect is maintained over time, but the manufacturing process becomes more complex

Engineering Contradiction:

Improvecoating layer durabilityVSAvoidcoating process complexity

Core Design Contradiction:

Duration of action of stationary objectVSEase of manufacture

Solution Approach 1:

The patent introduces a silicon oxide layer as an intermediary between the boric acid ester compound and the negative electrode active material. This intermediary layer simplifies the manufacturing process by providing a stable base that enhances adhesion, while simultaneously ensuring long-term durability of the coating layer during cycling.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 effectively suppresses the increase in internal resistance and maintains excellent cycle characteristics even after repeated high-rate charge and discharge cycles, ensuring the battery's performance is sustained over time.

Implementation Method 1

the coating portion is disposed on the surface of the negative electrode active material by using the chemical bond of C—O—C

Methodology Applied

Scientific EffectChemical bonding: Chemical Bonding

Implementation Method 2

the boric acid ester compound is adsorbed on the surface of the negative electrode active material by the adsorbing action of boron atoms

Methodology Applied

Scientific EffectAdsorption: Adsorption

Data Source

PatentUS10811678B2Negative electrode material and lithium secondary battery using same

Publication Date: 2020.10.20 TOYOTA JIDOSHA KK

AI summary

According to the present invention, there is provided a negative electrode material for a lithium secondary battery, including a negative electrode active material including a carbon material and having an ID/IG ratio of XPS of 0.2 to 0.74, and a coating portion disposed on a surface of the negative electrode active material. The coating portion has a boron atom and a crosslinking site having a bonding portion of C—O—C and interposed between the boron atom and the negative electrode active material. In an XPS spectrum, when an area of the peak of the 1s electron orbital of the boron atom is denoted by Ab and an area of the peak of the C—O—C bonding portion is denoted by Ac, the ratio Ac/Ab of the peak area Ac to the peak area Ab is 0.11 or more and 0.51 or less.