Multilayer Positive Electrode Structure for High-Pressure Rolling

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Solution Overview

Problem

Lithium secondary batteries face challenges with the use of nickel-rich lithium composite transition metal oxide positive electrode active materials due to particle cracking during the rolling process, leading to reduced compaction density and stability, which affects the battery's life characteristics and thermal stability.

Innovation Solution

A multilayer positive electrode structure is implemented, comprising a first layer of primary macroparticles and a second layer of both secondary microparticles and macroparticles with different average particle sizes, allowing for higher rolling pressures without causing short circuits and improving life characteristics by reducing cracking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of stationary object

If secondary macroparticles are used to increase compaction density, then compaction density improves, but particle cracking occurs during rolling process

Engineering Contradiction:

Improvecompaction densityVSAvoidparticle strength

Core Design Contradiction:

Volume of stationary objectVSStrength

Solution Approach 1:

The positive electrode active material is divided into two distinct size fractions: secondary macroparticles (D50: 7-20 μm) and secondary microparticles (D50: 1-7 μm). This segmentation allows each particle size to fulfill different functions - macroparticles provide compaction density while microparticles fill voids and reduce stress concentration, preventing cracking during rolling.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the electrode structure are assigned different particle sizes. The macroparticles form the primary framework for high compaction density, while microparticles are distributed throughout to fill interstices and provide local stress relief. This local quality differentiation optimizes both compaction and crack resistance.

Inventive Principle:

Principle #3Local quality

2Reliability

If rolling pressure is increased to prevent short circuit, then short circuit prevention improves, but particle cracking worsens

Engineering Contradiction:

Improveshort circuit preventionVSAvoidparticle strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

Secondary microparticles are introduced beforehand to act as a cushioning phase between macroparticles. During the rolling process, these microparticles absorb and distribute mechanical stress, preventing stress concentration at macroparticle interfaces that would otherwise lead to cracking under high rolling pressure.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The positive electrode active material is formulated as a composite system combining two particle size fractions (macroparticles and microparticles). This composite structure leverages the advantages of both particle sizes - macroparticles for structural integrity and microparticles for stress distribution - enabling high rolling pressure application without particle cracking.

Inventive Principle:

Principle #40Composite materials

3Quantity of substance

If nickel content is increased to ensure high capacity, then capacity improves, but chemical stability and thermal stability worsen

Engineering Contradiction:

ImprovecapacityVSAvoidchemical stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The particle size distribution parameters are optimized to control the behavior of high-nickel content material. By carefully controlling the D50 ranges of macroparticles (7-20 μm) and microparticles (1-7 μm), the electrode structure compensates for the inherent instability of high-nickel materials through reduced stress concentration and improved mechanical integrity during cycling.

Inventive Principle:

Principle #35Parameter changes

4Power

If bimodal-type positive electrode active materials are used to increase output, then output improves, but production of gas during cell operation increases

Engineering Contradiction:

ImproveoutputVSAvoidgas production

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

Inventive Principle:

Principle #40Composite materials

Data Source

PatentUS20240339597A1Positive Electrode for Lithium Secondary Battery and Positive Electrode and Lithium Secondary Battery Comprising the Same

Publication Date: 2024.10.10 LG ENERGY SOLUTION LTD

AI summary

A positive electrode for a lithium secondary battery includes a first positive electrode active material layer on the current collector and_a second positive electrode active material layer on the first positive electrode active material layer. The second positive electrode active material layer includes bimodal positive electrode active materials including positive electrode active material secondary macroparticles and secondary microparticles having different average particle sizes to allow sufficiently high rolling pressure when manufacturing the electrode. The first positive electrode active material in the first positive electrode active material layer interposed between the current collector and the second positive electrode active material layer has the positive electrode active material particles less vulnerable to cracking.