Layered Nickel-Rich Cathode Structure for Density and Stability
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Solution Overview
Problem
Lithium secondary batteries face challenges with cathode active materials that have low pressed density and reduced structural and electrochemical stability when nickel content is increased to improve capacity properties, leading to issues with resistance and operational reliability.
Innovation Solution
A cathode for lithium secondary batteries is designed with a multi-layered structure comprising a first cathode active material layer with bi-modal particles and a second layer with unimodal particles, both including lithium-nickel composite metal oxides, where the binder content is optimized to prevent migration and enhance adhesion, resulting in improved power and rapid-charge life-span properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If nickel content is increased to improve capacity properties, then energy density is improved, but structural and electrochemical stability are reduced
Solution Approach 1:
The cathode active material layer is divided into a first layer containing large-scaled particles (10-20 μm) and a second layer containing small-scaled particles (1-9 μm). This segmentation allows the larger particles to provide structural stability while smaller particles fill voids to maintain high density, resolving the contradiction between capacity and stability.
Solution Approach 2:
Different regions of the cathode are assigned different particle size characteristics. The first layer with larger particles provides mechanical integrity and structural stability, while the second layer with smaller particles maximizes space utilization and energy density. This local differentiation resolves the contradiction between structural stability and capacity.
2Quantity of substance
If nickel content is increased to improve capacity properties, then energy density is improved, but resistance properties are reduced
Solution Approach 1:
The cathode is segmented into two layers with different particle size distributions. The first layer with larger particles maintains structural integrity and resistance properties, while the second layer with smaller particles contributes to capacity without compromising overall resistance due to the stabilizing effect of the first layer.
Solution Approach 2:
The cathode uses a composite structure combining large-scaled and small-scaled particles in specific layers. This composite approach allows the system to achieve high capacity from the nickel-rich material while the multi-layer composite structure maintains resistance properties through optimized particle arrangement and binder distribution.
3Quantity of substance
If pressed density is improved, then energy density is improved, but structural stability is reduced
Solution Approach 1:
The cathode active material layer is segmented into a first layer with large-scaled particles (10-20 μm) that provide structural framework and stability, and a second layer with small-scaled particles (1-9 μm) that fill interstitial voids. This segmentation enables high pressed density while maintaining structural stability through the hierarchical particle arrangement.
Solution Approach 2:
Small-scaled particles are nested within the voids and interstices of the large-scaled particle structure. This nesting arrangement maximizes space utilization to achieve high pressed density while the larger particles maintain the overall structural framework and stability.
4Strength
If binder content is increased to improve adhesion, then adhesion is improved, but binder migration occurs leading to adhesion degradation
Solution Approach 1:
The binder is segmented and distributed differently in two layers. The first layer has a higher binder content (0.5-2 wt%) to ensure strong adhesion to the current collector, while the second layer has a lower binder content (0.1-0.5 wt%) to prevent migration. This segmentation resolves the contradiction between initial adhesion strength and long-term adhesion stability.
Solution Approach 2:
Different binder contents are applied locally in different layers. The first layer near the current collector has higher binder content for strong initial adhesion, while the second layer has lower binder content to prevent migration and maintain long-term adhesion stability. This local quality differentiation resolves the contradiction between adhesion strength and adhesion stability.
Data Source
AI summary
A cathode for a lithium secondary battery includes a cathode current collector, a first cathode active material layer on the cathode current collector and a second cathode active material layer on the first cathode active material layer. The first cathode active material layer includes first cathode active material particles and a first binder. The first cathode active material particles include large-scaled particles having an average diameter (D50) from 10 μm to 20 μm and small-scaled particles having an average (D50) diameter from 1 μm to 9 μm. The second cathode active material layer includes second cathode active material particles having an average diameter (D50) from 1 μm to 20 μm and a second binder.