Bilayer Positive Electrode Structure for Low-SOC Resistance Stability

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Solution Overview

Problem

Lithium secondary batteries with high nickel content positive electrodes experience increased resistance at low state-of-charge (SOC), leading to rapid degradation of output, which is a challenge for achieving high energy density and long driving ranges in electric vehicles.

Innovation Solution

A positive electrode with a bilayer active material structure, where the lower layer has a lower nickel content and the upper layer has a higher nickel content, is designed to control resistance, using specific chemical formulations and manufacturing methods to enhance structural stability and adhesion, thereby preventing resistance increases at low SOC.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a positive electrode with high nickel content is used to achieve high energy density, then the energy density is improved, but the resistance increases at low state-of-charge

Engineering Contradiction:

Improveenergy densityVSAvoidresistance stability at low SOC

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The positive electrode active material layer is divided into a lower layer and an upper layer with different nickel contents. The lower layer has lower nickel content (40-75 mol%) and the upper layer has higher nickel content (80-90 mol%), allowing each layer to contribute differently to resistance stability and energy density.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the positive electrode are assigned different nickel contents to optimize local properties. The lower layer near the current collector has lower nickel content for stability, while the upper layer has higher nickel content for energy density, creating spatially varying material properties.

Inventive Principle:

Principle #3Local quality

2Power

If a positive electrode with high nickel content is used to achieve high output, then the acceleration response is improved, but the resistance increases at low state-of-charge

Engineering Contradiction:

ImproveoutputVSAvoidresistance stability at low SOC

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The positive electrode is segmented into two layers with different nickel compositions. The lower layer provides structural stability and adhesion, while the upper layer provides high capacity, together enabling high output with stable resistance characteristics.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The positive electrode uses a composite structure combining two different positive electrode active materials with different nickel contents, creating a material system that exhibits both high power capability and stable resistance through the synergistic effect of the two layers.

Inventive Principle:

Principle #40Composite materials

Data Source

PatentUS20240014392A1Positive electrode and lithium secondary battery including the same

Publication Date: 2024.01.11 LG ENERGY SOLUTION LTD

AI summary

Disclosed is a positive electrode including: a positive electrode current collector; and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer has a lower layer region facing the positive electrode current collector and containing a first positive electrode active material and a first binder polymer, and an upper layer region facing the lower layer region and containing a second positive electrode active material and a second binder polymer, and the Ni content of the second positive electrode active material in the upper layer region is larger than the Ni content of the first positive electrode active material in the lower layer region. Also disclosed is a lithium secondary battery including the positive electrode.