Composite Positive Electrode Structure for High-Pressure Li Battery Cathodes
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Solution Overview
Problem
Existing lithium secondary batteries face challenges in achieving high safety, energy density, and rate characteristics due to the use of current collectors that do not effectively manage stress and pressure during manufacturing, leading to potential cracking and reduced performance.
Innovation Solution
A positive electrode design incorporating a current collector film with a resin layer and metal layer on both surfaces, combined with specific particle sizes and ratios of active material particles and binders, enhances safety and performance by allowing for better stress management and higher energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional current collector is used, then the manufacturing process is simple, but the electrode exhibits cracking under pressing pressure and shows poor rate characteristics
Solution Approach 1:
The current collector is divided into a resin layer and metal layers, with the resin layer segmented into multiple regions (first resin layer and second resin layer) with different properties. This segmentation allows different parts of the current collector to perform different functions: the first resin layer provides structural support while the second resin layer facilitates stress release, preventing electrode cracking without requiring excessive metal content.
Solution Approach 2:
The current collector uses a composite structure combining resin and metal materials. The resin layer (particularly the second resin layer with specific mechanical properties) is combined with metal layers to create a composite current collector that optimizes both mechanical strength and electrical conductivity, resolving the contradiction between electrode integrity and structural complexity.
2Quantity of substance
If pressing pressure is increased to improve energy density, then more active material can be packed, but the electrode characteristics deteriorate due to cracking
Solution Approach 1:
The second resin layer in the current collector acts as a cushioning layer that is designed to release stress before it can propagate into the electrode mixture layer. This beforehand cushioning prevents cracking during pressing, allowing higher pressing pressures to be applied to increase active material content without deteriorating electrode characteristics.
3Quantity of substance
If larger active material particles are used, then energy density improves, but rate characteristics deteriorate
Solution Approach 1:
The electrode mixture layer uses active material particles with a specific size distribution where larger particles (D50: 10 μm or more and 25 μm or less) provide high energy density, while the presence of smaller particles fills voids and improves contact. This local quality variation in particle sizes allows the electrode to achieve both high energy density and favorable rate characteristics.
Data Source
AI summary
The present disclosure relates to a positive electrode for a lithium secondary battery, which includes a current collector film including a resin layer and a metal layer provided on each of both surfaces of the resin layer and a positive electrode mixture layer formed on the current collector film, in which the positive electrode mixture layer contains first positive-electrode active material particles having a median diameter D50 of 10 μm or more and 25 μm or less, second positive-electrode active material particles, and two or more kinds of binders, a median diameter D50 ratio of the second positive-electrode active material particles to the first positive-electrode active material particles is 0.75 or less, and a mass ratio of the first positive-electrode active material particles to the second positive-electrode active material particles in the positive electrode ([a content of the first positive-electrode active material particles in the positive electrode]/[a content of the second positive-electrode active material particles in the positive electrode]) is 1.5 or more and 9.0 or less.