Phosphate-Coated Ni-Mn Cathode Material for High-SOC Resistance
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Solution Overview
Problem
Raising the charge voltage in non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, increases the resistance of the positive electrode, particularly in the high state of charge (SOC) region, which affects the battery's efficiency and durability.
Innovation Solution
Incorporating a lithium-transition metal composite oxide with specific particle characteristics, including Ni and Mn as main components, and coating its surfaces with pyrophosphoric acid or a phosphate salt, such as lithium pyrophosphate, to inhibit resistance increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the charge voltage is raised to increase capacity and enable quick charge, then the battery capacity and charging speed are improved, but the resistance of the positive electrode increases particularly in the high SOC region
Solution Approach 1:
A coating layer containing at least one of Li2SiO3 and Li4SiO4 is formed on the surface of the lithium-transition metal composite oxide particles. This coating layer acts as an intermediary between the electrode material and the electrolyte, suppressing resistance increase during high-voltage charging while maintaining ion transport efficiency
Solution Approach 2:
The invention controls specific parameters including particle size (D50: 3.0-6.0 μm), crystallite size (400-1500 Å), and coating layer thickness (0.1-5 nm) to optimize the balance between capacity and resistance. By precisely controlling these parameters, the electrode maintains low resistance even at high charge voltages
2Quantity of substance
If the charge voltage is raised to increase capacity, then the energy storage is improved, but the increase in resistance with cycles becomes more significant
Solution Approach 1:
The coating layer of Li2SiO3 and Li4SiO4 is formed preliminarily on the electrode particles before battery assembly. This pre-formed protective layer prevents degradation reactions during initial cycling, thereby suppressing resistance increase throughout the battery's service life and improving long-term cycle stability
Solution Approach 2:
The invention uses a composite structure combining lithium-transition metal composite oxide core particles with a Li2SiO3-Li4SiO4 coating shell. This composite material structure provides both high capacity (from the Ni-rich core) and excellent cycle stability (from the protective silicate shell), resolving the contradiction between capacity and durability
Data Source
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AI summary
An example of a positive electrode active material according to one embodiment includes a lithium transition metal composite oxide that contains at least 80 mol% of Ni and Mn with respect to the total molar amount of metal elements other than Li. The lithium transition metal composite oxide is composed of one primary particle, or particles composed of 2 to 100 primary particles, and has a D50 of 0.6 µm to 4.0 µm, and a crystallite size of 370 Å to 1,500 Å. On a particle surface of the composite oxide, at least one selected from among a pyrophosphoric acid and a phosphate salt is present in an amount of 0.1 mol% to 5.0 mol%.