Nickel Cathode Precursor Phosphate Core for Cycle-Life Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Nickel-based lithium transition metal oxides in rechargeable lithium batteries face issues with unstable crystal structure, leading to storage characteristics, cycle-life characteristics, and stability problems, which are not adequately addressed by existing surface coatings.
Innovation Solution
A nickel-based composite precursor is developed with a central portion containing lithium transition metal phosphate and a surface portion without phosphate, coated with a thin layer of lithium transition metal phosphate, enhancing lithium ion conductivity and preventing electrolyte reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a nickel-based lithium transition metal oxide is used as positive active material, then high capacity characteristics are achieved, but unstable crystal structure leads to poor storage and cycle-life characteristics
Solution Approach 1:
The patent uses a composite coating structure consisting of an inner layer (Li-M-O spinel or olivine phase) and an outer layer (amorphous or crystalline glassy carbon). This multi-layer composite structure combines the benefits of lithium ion conductivity from the inner layer with surface protection and stability from the outer carbon layer, resolving the contradiction between high capacity and poor cycle-life characteristics
Solution Approach 2:
The coating structure is designed with different properties at different locations: the inner layer is positioned at the grain boundaries and surface regions where lithium ion transport occurs, while the outer carbon layer covers the external surface to provide stability. This spatial differentiation of material properties addresses both capacity and stability requirements in different regions
2Reliability
If phosphate coating material is applied to coat secondary oxide particles, then surface stability is improved, but large particle size prevents uniform coating on grain boundaries
Solution Approach 1:
The coating process is segmented into two distinct stages: first forming an inner layer at grain boundaries through controlled precipitation, then forming an outer layer on the external surface. This segmentation allows each layer to be optimized independently for its specific function, achieving both uniform grain boundary coating and surface stability
Solution Approach 2:
The inner layer is formed preliminarily before the outer layer through a controlled precipitation process using phosphate-containing solution. This preliminary formation of the inner layer at grain boundaries ensures uniform distribution before the outer surface coating is applied, solving the uniformity problem
Data Source
AI summary
An embodiment provides a positive active material precursor for a rechargeable lithium battery including: a nickel-based composite precursor including a secondary particle comprising a plurality of primary particles that are aggregated together, the nickel-based composite precursor having a central portion and a surface portion, and the central portion of the nickel-based composite precursor including a phosphate.