Silicon Anode Electrode with Protective Layer for Cycle Stability

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Solution Overview

Problem

Lithium-ion secondary batteries face challenges with cycle characteristics due to structural destruction and reactivity of the anode active material layer with the electrolyte, particularly when using silicon or germanium as the anode material, leading to capacity loss and poor durability.

Innovation Solution

The use of a current collector made from metals like copper, nickel, titanium, or chromium, combined with a thin film layer of copper or nickel, which prevents intermetallic compound formation with lithium and inhibits the active material layer's reaction with the electrolyte, thereby enhancing the structural integrity and cycle performance of the anode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon or germanium is used as the anode active material to increase battery capacity, then the battery capacity is improved, but the active material layer undergoes intense expansion and shrinkage during charge and discharge, causing structural destruction and poor cycle characteristics

Engineering Contradiction:

Improvebattery capacityVSAvoidcycle characteristics

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The anode is segmented into multiple functional layers: current collector, buffer layer, active material layer, and protective layer. This segmentation allows each layer to perform its specific function - the buffer layer absorbs expansion stress while the protective layer prevents electrolyte contact, resolving the contradiction between high capacity and cycle stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The anode uses a composite structure combining different materials (current collector, buffer layer material, active material, protective layer material) with complementary properties. This composite approach enables simultaneous achievement of high capacity (from Si/Ge active material) and good cycle characteristics (from protective buffer layers).

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If the active material layer is made thin to reduce electrolyte reaction, then cycle characteristics are improved, but the surface area to volume ratio increases, promoting decomposition reaction of the electrolytic solution

Engineering Contradiction:

Improvecycle characteristicsVSAvoidelectrolyte decomposition

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The protective layer and buffer layer act as intermediary layers between the active material layer and the electrolyte. These intermediary layers prevent direct contact between the active material and electrolyte, reducing decomposition reactions while maintaining the thin active material layer configuration for good cycle characteristics.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If a conventional coating-type anode with slurry containing particle active material and binder is used, then manufacturing is easier, but the anode falls off due to expansion and shrinkage, and fine particles are generated, deteriorating current collecting characteristics

Engineering Contradiction:

Improvecoating process simplicityVSAvoidcurrent collecting characteristics

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent employs thin film technology to create a dense, integrated active material layer directly on the current collector. This thin film structure is more flexible and adherent than conventional slurry coatings, preventing fall-off during expansion/shrinkage cycles and eliminating fine particle generation, thus improving current collecting characteristics while maintaining manufacturability.

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

This configuration significantly improves the cycle characteristics of the battery by preventing structural destruction and reactivity issues, leading to better capacity retention and extended lifespan.

Implementation Method 1

a thin film layer containing at least one of copper and nickel provided on the active material layer

Methodology Applied

Scientific EffectPhysical barrier protection:

Implementation Method 2

a current collector containing at least one from the group consisting of copper (Cu), nickel (Ni), titanium (Ti), iron (Fe), and chromium (Cr)

Methodology Applied

Scientific EffectMechanical support:

Data Source

PatentUS7838147B2Electrode and battery using it

Publication Date: 2010.11.23 MURATA MFG CO LTD

AI summary

The invention provides an electrode which can improve cycle characteristics by reducing structural destruction of an active material layer and reaction between the active material layer and an electrolyte according to charge and discharge, and a battery using it. A current collector made of a metal material containing a metal element which does not form an intermetallic compound with Li, such as Cu, Ni, Ti, Fe, and Cr; the active material layer containing Si, Ge, or an alloy thereof, and a thin film layer made of a metal material containing at least one of metal elements and metalloid elements which can make a solid solution with lithium and do not form an intermetallic compound with lithium, e.g. Cu, Ni are layered in this order. The current collector is alloyed with the active material layer, and the thin film layer is alloyed with the active material layer.