SiOx Negative Electrode with Bump-Structured Current Collector

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Solution Overview

Problem

Lithium secondary batteries with silicon or tin negative electrodes face deformation and peeling issues due to volumetric changes during charging and discharging, leading to poor charge-discharge cycle characteristics and efficiency.

Innovation Solution

A negative electrode design featuring a current collector with bumps, a first active material layer of SiOx (0<x<1) covering the surface, and active material particles located on these bumps, enhancing adhesion and providing spaces for expansion to alleviate stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If pillar-like active material particles are selectively formed on the current collector surface, then expansion stress can be alleviated and deformation reduced, but charge-discharge efficiency deteriorates due to lithium deposition on exposed current collector portions

Engineering Contradiction:

Improvecycle characteristicsVSAvoidcharge-discharge efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

A buffer layer is introduced as an intermediary between the active material particles and the current collector. This buffer layer fills the spaces between the pillar-like particles and covers the exposed current collector surface, preventing lithium deposition on the current collector while maintaining the expansion relief structure. The buffer layer acts as a mediator that resolves the conflict between cycle stability and charge-discharge efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If active material particles are formed directly on the current collector, then adhesion is strong, but expansion stress causes peeling during repeated charging and discharging

Engineering Contradiction:

ImproveadhesionVSAvoidcycle characteristics

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The buffer layer serves as a mediator between the active material particles and the current collector. It provides adhesion while accommodating expansion stress through its own deformability, preventing the peeling that occurs when active material is directly bonded to the rigid current collector.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The buffer layer functions as a flexible thin film that can deform to accommodate the volumetric changes of active material particles during lithium insertion and extraction, while maintaining connection to the current collector and preventing peeling.

Inventive Principle:

Principle #30Flexible shells and thin films

3Productivity

If the current collector surface is fully covered with active material, then charge-discharge efficiency is high, but expansion stress causes deformation and wrinkles

Engineering Contradiction:

Improvecharge-discharge efficiencyVSAvoidelectrode deformation

Core Design Contradiction:

ProductivityVSShape

Solution Approach 1:

The current collector surface is designed with non-uniform coverage: pillar-like active material particles are formed at specific locations (bumps) while buffer layer covers other areas. This local differentiation allows regions of high lithium reactivity (particles) to coexist with regions that accommodate expansion (buffer layer), preventing overall electrode deformation.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The active material layer is segmented into discrete pillar-like particles rather than a continuous film. This segmentation creates voids between particles that can accommodate expansion, while the buffer layer fills these voids to prevent current collector exposure. The segmented structure resolves the conflict between efficiency and deformation.

Inventive Principle:

Principle #1Segmentation

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 design improves adhesion, reduces peeling, and enhances charge-discharge cycle characteristics by managing expansion stress, leading to better capacity retention and efficiency.

Implementation Method 1

a first active material layer which covers the surface of the current collector and has a chemical composition represented as SiOx

Methodology Applied

Scientific EffectAdhesion: Adhesive

Implementation Method 2

The aforementioned negative-electrode active materials undergo significant volumetric changes when reacting with lithium ions. Therefore, at the time of charging and discharging, the negative-electrode active material will undergo significant expansion/contraction

Methodology Applied

Scientific EffectVolumetric change: Thermal Expansion

Implementation Method 3

Each of the plurality of active material particles is located on a corresponding bump of the current collector... spaces for alleviating the expansion stress of silicon can be guaranteed between active material particles

Methodology Applied

Scientific EffectStress relief: Stress Relaxation

Data Source

PatentUS8771874B2Negative electrode contacting silicon oxide active material layers for lithium secondary battery and method for producing the same

Publication Date: 2014.07.08 PANASONIC HOLDINGS CORP

AI summary

The negative electrode for a lithium secondary battery includes: a current collector 11 having a plurality of bumps 11a on a surface thereof; a first active material layer formed on the current collector 11; and a second active material layer 15 disposed on the first active material layer 12 and including a plurality of active material particles 14. Each of the plurality of active material particles 14 is located on a corresponding bump 11a of the current collector 11, and each of the first active material layer 12 and the plurality of active material particles 14 has a chemical composition represented as SiOx (0<x<1).