Layered High-Ni Cathode Structure for Low-Gas Li-Ion Batteries

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Nonaqueous electrolyte secondary batteries with high Ni content lithium complex oxides experience excessive gas generation under high voltage due to stress-induced cracking of the positive electrode active material, leading to side reactions with the electrolyte.

Innovation Solution

A multilayer positive electrode structure is implemented, with a dense first layer and a porous second layer containing a covering element like boron, where the second layer's porosity and covering element distribution minimize stress and side reactions, reducing gas generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If high Ni content lithium complex oxide (70 mol % or more) is used as positive electrode active material to improve energy density, then energy density is improved, but gas generation increases under high voltage due to stress-induced cracking

Engineering Contradiction:

Improveenergy densityVSAvoidgas generation

Core Design Contradiction:

Use of energy by moving objectVSObject-generated harmful factors

Solution Approach 1:

The positive electrode active material layer is divided into a first layer (closer to current collector) and a second layer (farther from current collector). The first layer uses high Ni content lithium complex oxide with low porosity (<2%) to provide high energy density, while the second layer uses high Ni content lithium complex oxide with controlled porosity (2-20%) and covering element to suppress gas generation. This segmentation allows each layer to perform its specific function optimally.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the positive electrode active material layer are given different properties. The first layer has low porosity for high energy density, while the second layer has controlled porosity (2-20%) and contains a covering element (0.5-3 mol %) to reduce gas generation. This local differentiation of material properties resolves the contradiction between energy density and gas generation.

Inventive Principle:

Principle #3Local quality

2Use of energy by moving object

If positive electrode is pressed with high pressure to increase energy density, then energy density is improved, but cracking occurs in positive electrode active material on front surface side

Engineering Contradiction:

Improveenergy densityVSAvoidcrack resistance

Core Design Contradiction:

Use of energy by moving objectVSStrength

Solution Approach 1:

The positive electrode active material layer is segmented into two layers with different porosity characteristics. The first layer (near current collector) has low porosity (<2%) to withstand pressing pressure, while the second layer (front surface) has controlled porosity (2-20%) that provides crack resistance. This segmentation allows high pressure pressing to increase energy density without causing cracking in the front surface active material.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The second layer with controlled porosity (2-20%) acts as a cushioning layer that absorbs pressing stress before it reaches the front surface active material. This beforehand cushioning prevents cracking in the front surface active material while still allowing high pressure pressing to achieve high energy density in the first layer.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Strength

If porosity of high Ni content lithium complex oxide is increased to reduce cracking, then crack resistance is improved, but energy density decreases

Engineering Contradiction:

Improvecrack resistanceVSAvoidenergy density

Core Design Contradiction:

StrengthVSUse of energy by moving object

Solution Approach 1:

The positive electrode active material layer is divided into two layers with different porosity values. The first layer has low porosity (<2%) to maximize energy density, while the second layer has controlled porosity (2-20%) to provide crack resistance. This segmentation resolves the contradiction by assigning different porosity requirements to different functional regions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different porosity levels are applied locally to different layers. The first layer (near current collector) has low porosity for high energy density, while the second layer (front surface) has higher porosity (2-20%) for crack resistance. This local quality differentiation allows both high energy density and crack resistance to be achieved simultaneously.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20230369574A1Nonaqueous electrolyte secondary battery

Publication Date: 2023.11.16 PRIME PLANET ENERGY & SOLUTIONS INC

AI summary

A positive electrode of a nonaqueous electrolyte secondary battery disclosed herein includes a positive electrode active material layer with a multilayer structure including a positive electrode lower layer and a positive electrode upper layer. The positive electrode lower layer includes a first positive electrode active material including a first Ni content lithium complex oxide. The positive electrode upper layer includes a second positive electrode active material including a second Ni content lithium complex oxide, and does not include a larger space than an average cross-sectional area of the primary particles inside the secondary particle, and a covering element. The ratio of the covering element is 0.5 to 3 mol % when the total of metal elements of the second Ni content lithium complex oxide is 100 mol %.