Silicon-Graphite Negative Electrode for Lithium-Ion Battery

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Solution Overview

Problem

Conventional non-aqueous electrolyte secondary batteries using graphite and alloying materials like silicon or tin face challenges in maintaining electrical conductivity and cycle life due to the expansion of alloying materials, leading to separation from the current collector and degradation of battery characteristics.

Innovation Solution

A negative electrode composition comprising a combination of graphite and an alloying material with an A phase mainly composed of Si and a B phase as an intermetallic compound of a transition metal element, where at least one phase includes microcrystalline or amorphous regions, with specific weight ratios and particle size distributions to minimize expansion and maintain electronic conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If alloying materials (silicon or tin) are used to increase capacity, then the discharge capacity increases significantly, but the volume expansion causes separation from current collector and degradation of battery characteristics

Engineering Contradiction:

Improvedischarge capacityVSAvoidbattery characteristics

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The invention uses a composite material consisting of alloying material particles (silicon or tin) combined with conductive graphite particles. The graphite serves as a conductive matrix that maintains electrical connectivity while accommodating the volume expansion of the alloying material, thus preventing separation from the current collector and maintaining battery characteristics throughout charge/discharge cycles.

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If graphite and alloying material are simply mixed to achieve higher capacity, then the capacity increases, but the uneven expansion of alloying material moves graphite particles causing separation and lowering electronic conductivity

Engineering Contradiction:

ImprovecapacityVSAvoidelectronic conductivity loss

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The invention introduces conductive graphite particles as an intermediary substance between alloying material particles. The graphite acts as a conductive matrix that fills the spaces between alloying material particles and maintains electrical connectivity during volume expansion, preventing the separation and conductivity loss that would occur with simple mixing.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If particle size of silicide is controlled to lessen expansion impact, then some improvement in characteristics is achieved, but cracking of alloying material particles still occurs causing current collector property degradation

Engineering Contradiction:

Improvebattery characteristicsVSAvoidcurrent collector property degradation

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The conductive graphite particles form a flexible conductive network around the alloying material particles. This graphite matrix can accommodate the volume expansion and cracking of alloying material particles without losing electrical connectivity, thus preventing degradation of current collector properties while maintaining battery characteristics.

Inventive Principle:

Principle #30Flexible shells and thin films

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 deterioration of battery characteristics, enabling a non-aqueous electrolyte secondary battery with high capacity and excellent cycle characteristics by maintaining the structural integrity and conductivity of the alloying material.

Implementation Method 1

Metal elements, such as silicon and tin, are capable of electrochemically absorbing and desorbing lithium ions

Methodology Applied

Scientific EffectElectrochemical absorption: Absorption (physical)

Implementation Method 2

lithium is intercalated between the layers of graphite (intercalation reaction)

Methodology Applied

Scientific EffectIntercalation reaction: Absorption (physical)

Implementation Method 3

The formation of a lithium alloy involves a very large expansion caused by the change in its crystal structure. For example, the volume of silicon theoretically expands 4.1-fold when it absorbs lithium to its maximum.

Methodology Applied

Scientific EffectVolume expansion: Thermal Expansion

Data Source

PatentUS7635540B2Negative electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery comprising the same

Publication Date: 2009.12.22 PANASONIC HOLDINGS CORP

AI summary

A negative electrode containing an alloying material and a graphite material for providing a non-aqueous electrolyte secondary battery with a high capacity and excellent cycle characteristics. The negative electrode includes graphite and an alloying material capable of electrochemically absorbing and desorbing Li. The alloying material includes an A phase composed mainly of Si and a B phase including an intermetallic compound of a transition metal element and Si. The A phase and/or the B phase include a microcrystalline or amorphous region. The weight percentage of the A phase relative to the total weight of the A phase and the B phase is greater than 40% and not greater than 95%. The weight percentage of the graphite relative to the total weight of the alloying material and the graphite is not less than 50% and not greater than 95%.