Silicon Negative Electrode with Lattice-Matched Matrix

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Solution Overview

Problem

Lithium ion secondary batteries using silicon as the negative electrode active material face issues with volume expansion, conductivity degradation, and rapid capacity loss due to cracking, which limits their practical application and cycle stability.

Innovation Solution

A silicon-based negative electrode active material with a three-layer or two-layer structure is developed, featuring a crystalline Si main phase and a matrix with a lattice mismatch ratio of 12% or less, incorporating an amorphous phase and crystal phases with different structures to suppress volume change and enhance coherence at the interface, thereby maintaining capacity and conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon is used as the negative electrode active material to achieve high capacity and high energy density, then the battery capacity and energy density are improved, but the cycle stability and reliability deteriorate due to volume expansion and cracking

Engineering Contradiction:

Improvebattery capacityVSAvoidcycle stability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The silicon-based negative electrode active material is divided into a multi-phase structure consisting of a Si main phase and a matrix phase with different crystal structures. This segmentation allows the silicon to undergo volume expansion during charging while the matrix provides structural support, preventing cracking and maintaining cycle stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite material structure where silicon is combined with a matrix having a crystal structure different from silicon's diamond cubic structure. This composite approach leverages the high capacity of silicon while the matrix provides mechanical stability and prevents the degradation issues associated with pure silicon.

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If the volume of silicon is expanded to occlude more lithium ions for high capacity, then the lithium ion storage capacity is improved, but the conductivity and structural integrity deteriorate due to cracking

Engineering Contradiction:

Improvelithium ion storage capacityVSAvoidstructural integrity

Core Design Contradiction:

Quantity of substanceVSStrength

Solution Approach 1:

The matrix phase with a crystal structure different from silicon is introduced beforehand to cushion and accommodate the volume expansion of silicon during lithium ion occlusion. This pre-designed structural buffer prevents cracking and maintains conductivity by allowing controlled expansion without structural failure.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If a thin film coating is applied to silicon to control reaction speed and improve stability, then the cycle efficiency is improved, but the electrochemical characteristic deteriorates when the film thickness is large due to increased resistance

Engineering Contradiction:

Improvecycle efficiencyVSAvoidelectrochemical characteristic

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

Instead of applying a thick protective film that increases resistance, the invention changes the fundamental parameter of the matrix material's crystal structure to provide stability. The matrix with a different crystal structure inherently controls the reaction speed and provides structural support without introducing the resistance issues associated with thick coating films.

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 structured negative electrode active material exhibits reduced volume expansion, improved cycle stability, and maintained capacity over 50 cycles, effectively addressing the limitations of silicon-based batteries by controlling lattice mismatch and interface coherence.

Implementation Method 1

at least a part of the matrix has a crystal lattice parameter which is any one among n times, 1/n time, n√2 times, n/√2 times, and n√5 times of a crystal lattice parameter of the Si main phase

Methodology Applied

Scientific EffectLattice matching:

Implementation Method 2

lithium (ions) generated in a positive electrode active material is transferred to a negative electrode active material through an electrolyte and is intercalated into a layer structure of the negative electrode active material during charging and is deintercalated in the negative electrode active material during discharging

Methodology Applied

Scientific EffectIntercalation:

Data Source

PatentUS11050056B2Negative active material for secondary battery and secondary battery including the same

Publication Date: 2021.06.29 ILJIN ELECTRONICS

AI summary

The present invention relates to a negative electrode active material for a secondary battery, including: a Si main phase formed of crystalline Si; and a matrix coexisting with the Si main phase, in which at least a part of the matrix has a crystal lattice parameter which is any one among n times, 1/n time, n√2 times, n/√2 times, and n√5 times of a crystal lattice parameter of the Si main phase (n is an integer).