Composite Negative Electrode Material for Lithium Secondary Batteries

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Solution Overview

Problem

Lithium secondary batteries with lithium metal as the negative electrode suffer from dendrite formation, leading to internal short circuits and poor charge/discharge efficiency due to high reactivity and volume expansion issues with materials like silicon, tin, and zinc, resulting in low reliability and short cycle life.

Innovation Solution

A composite negative electrode material comprising solid phases A and B, where phase A includes silicon, tin, or zinc, and phase B is a solid solution or intermetallic compound with elements from Group 2, transition, Group 12, Group 13, and Group 14, optimized to suppress cracking through controlled X-ray diffraction intensity and peak width, enhancing electronic conductivity and cycle stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If lithium metal is used as the negative electrode material, then the energy density is improved, but dendrite deposits form on the negative electrode during charging causing internal short circuits

Engineering Contradiction:

Improveenergy densityVSAvoidreliability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

An artificial solid-electrolyte interface layer is introduced as an intermediary between the lithium metal negative electrode and the electrolyte. This layer acts as a protective mediator that prevents direct contact between lithium and electrolyte, thereby suppressing dendrite formation and internal short circuits while maintaining the high energy density benefits of lithium metal

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stress or pressure

If the deposited dendrite reacts with the solvent in the electrolyte, then the internal resistance increases, but the charge/discharge efficiency decreases

Engineering Contradiction:

Improveinternal resistanceVSAvoidcharge/discharge efficiency

Core Design Contradiction:

Stress or pressureVSProductivity

Solution Approach 1:

An artificial solid-electrolyte interface layer is formed beforehand on the lithium metal surface to cushion and prevent the harmful reaction between deposited dendrite and electrolyte solvent. This pre-formed protective layer eliminates the formation of high-resistance byproducts that would otherwise increase internal resistance and reduce charge/discharge efficiency

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Quantity of substance

If silicon, tin or zinc is used as the negative electrode material, then the theoretical capacity is improved, but volume expansion causes cracking and pulverization

Engineering Contradiction:

Improvetheoretical capacityVSAvoidstrength

Core Design Contradiction:

Quantity of substanceVSStrength

Solution Approach 1:

The crystal structure parameters of silicon, tin or zinc are modified by introducing alloying elements (such as aluminum, copper, or other metals) to create intermetallic compounds or solid solutions. This parameter change reduces the volume expansion ratio during lithium insertion/extraction, preventing cracking and pulverization while maintaining high theoretical capacity

Inventive Principle:

Principle #35Parameter changes

4Quantity of substance

If simple substance metals or non-metals are used as the negative electrode material, then the electrochemical capacity is improved, but the charge/discharge cycle characteristics deteriorate

Engineering Contradiction:

Improveelectrochemical capacityVSAvoidcharge/discharge cycle characteristics

Core Design Contradiction:

Quantity of substanceVSDuration of action of stationary object

Solution Approach 1:

Simple substance metals or non-metals (such as silicon, tin, or zinc) are combined with other elements to form composite materials like intermetallic compounds or solid solutions. This composite structure provides both high electrochemical capacity and excellent charge/discharge cycle characteristics by reducing volume expansion and improving structural stability

Inventive Principle:

Principle #40Composite materials

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 negative electrode material significantly improves cycle life and capacity retention by reducing stress and pulverization, maintaining high discharge capacity and efficiency even after multiple cycles.

Implementation Method 1

a negative electrode material for non-aqueous electrolyte secondary batteries capable of absorbing and desorbing lithium

Methodology Applied

Scientific EffectIntercalation: Absorption (physical)

Implementation Method 2

the ratio (IA/IB) of the maximum diffracted X-ray intensity (IA) attributed to the solid phase A to the maximum diffracted X-ray intensity (IB) attributed to the solid phase B satisfies 0.001≦IA/IB≦0.1, in terms of a diffraction line obtained by a wide-angle X-ray diffraction measurement

Methodology Applied

Scientific EffectX-ray diffraction: X-Ray

Data Source

PatentUS7736806B2Cathode material and non-aqueous electrolyte secondary battery using it

Publication Date: 2010.06.15 PANASONIC HOLDINGS CORP

AI summary

A negative electrode material for non-aqueous electrolyte secondary batteries, characterized in that the negative electrode material comprises a composite particle including solid phases A and B, the solid phase A being dispersed in the solid phase B, and the ratio (IA/IB) of the maximum diffracted X-ray intensity (IA) attributed to the solid phase A to the maximum diffracted X-ray intensity (IB) attributed to the solid phase B satisfies 0.001≦IA/IB≦0.1, in terms of a diffraction line obtained by a wide-angle X-ray diffraction measurement of the composite particle.