Positive Electrode Mixture Layer With Low-Hardness Buffering
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Solution Overview
Problem
The density of the positive electrode mixture layer in secondary batteries does not increase beyond a certain limit, even with increased linear pressure during rolling, leading to cracks in the active material and increased battery resistance.
Innovation Solution
Incorporating two or more types of positive electrode active materials and a low-hardness compound with a lower hardness than the active materials into the positive electrode mixture layer, with a content of the low-hardness compound between 0.05 and 1.00 parts by mass per 100 parts by mass of active materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If linear pressure during rolling is increased to increase density of positive electrode mixture layer, then density is improved, but cracks are caused in active material and battery resistance increases
Solution Approach 1:
A low-hardness compound (Mohs hardness 1-3) is introduced as an intermediary substance between the positive electrode active material particles. This mediator prevents direct hard-on-hard contact during rolling, reducing crack formation while allowing sufficient pressure to achieve high density. The low-hardness compound acts as a buffer that absorbs mechanical stress without transmitting it to the brittle active material.
Solution Approach 2:
The hardness parameter of the electrode mixture is modified by adding a low-hardness compound with Mohs hardness of 1-3, which is significantly softer than the active material (Mohs hardness 5-8). This parameter change allows the mixture to be more compliant under rolling pressure, achieving high density without causing cracks in the active material particles.
2Volume of stationary object
If linear pressure during rolling is increased to increase density of positive electrode mixture layer, then density is improved, but manufacturing precision deteriorates due to crack formation
Solution Approach 1:
The low-hardness compound serves as a protective intermediary that prevents mechanical damage to the active material during the rolling process. By placing softer particles between the harder active material particles, the system achieves high compaction density while maintaining particle integrity and avoiding cracks that would compromise manufacturing precision.
Solution Approach 2:
The low-hardness compound is mixed into the electrode mixture beforehand, providing pre-positioned cushioning elements that will absorb rolling pressure before it reaches the active material. This beforehand cushioning prevents crack formation during the subsequent rolling process, ensuring both high density and structural integrity.
Data Source
AI summary
Provided are: a high-density positive electrode capable of suppressing battery resistance; and a secondary battery using said positive electrode. A positive electrode for a secondary battery according to one aspect of the present disclosure has a positive electrode current collector and a positive electrode mixture layer provided on the surface of the positive electrode current collector, wherein: the positive electrode mixture layer includes n types of positive electrode active materials (n is an integer of 2 or more) and a low-hardness compound having a lower hardness than any of the n types of positive electrode active materials; and the content of the low-hardness component in the positive electrode mixture layer is more than 0.05 parts by mass and less than 1.00 parts by mass with respect to 100 parts by mass of the positive electrode active material.