Li-ion Battery Cathode Surface Modification for Thermal Stability
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Solution Overview
Problem
Conventional lithium ion secondary batteries face challenges in increasing charge-discharge capacity while maintaining low resistance and cycle durability, as the substitution of Ni with other elements can lead to decreased capacity and increased resistance, and excessive surface modification with lithium-titanium composite oxide can hinder lithium ion insertion and desorption.
Innovation Solution
A positive-electrode material with a lithium complex compound represented by the formula Li1+aNibMncCodTieMfO2+α, where the atomic ratio Ti3+/Ti4+ is between 1.5 and 20, and specific stoichiometric ratios of Li, Ni, Mn, Co, and Ti are optimized to enhance charge-discharge capacity and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ni is substituted with other elements to improve thermal stability, then thermal stability is improved, but charge-discharge capacity decreases
Solution Approach 1:
The patent applies local quality by creating a surface-modified structure where only the surface layer contains lithium-titanium composite oxide, while the core maintains high Ni content for capacity. This allows the surface to provide thermal stability and structural integrity, while the core delivers high charge-discharge capacity through Ni-based redox reactions.
Solution Approach 2:
The patent uses composite materials by combining lithium-containing composite oxide particles with lithium-titanium composite oxide to form a surface-modified composite structure. This composite approach enables the material to simultaneously exhibit the high capacity characteristics of Ni-rich materials and the thermal stability of lithium-titanium composite oxide.
2Reliability
If excessive surface modification with lithium-titanium composite oxide is applied to improve safety, then thermal stability is improved, but lithium ion insertion and desorption are hindered
Solution Approach 1:
The patent applies partial action by controlling the lithium-titanium composite oxide content to be within a specific range (0.01 to 1.95 mol % relative to base material). This partial modification provides sufficient thermal stability and safety improvements without creating an excessively thick surface layer that would block lithium ion diffusion pathways.
Solution Approach 2:
The patent uses parameter changes by precisely controlling the titanium content parameter within optimal ranges and adjusting heat treatment parameters (400 to 1000° C.) to achieve the desired surface modification degree. These parameter optimizations ensure adequate safety while maintaining lithium ion conductivity.
3Duration of action of stationary object
If titanium content in surface layer is increased to improve cycle durability, then cycle characteristics are improved, but charge-discharge capacity decreases
Solution Approach 1:
The patent applies partial action by limiting titanium content to specific ranges (0.01 to 1.95 mol % relative to base material, with preferred ranges of 0.05 to 0.5 mol %). This partial titanium incorporation provides sufficient cycle durability improvement through enhanced surface stability without excessively reducing the Ni content available for charge-discharge reactions.
Solution Approach 2:
The patent optimizes the titanium content parameter within defined ranges to achieve the best balance between cycle durability and charge-discharge capacity. By controlling titanium content and heat treatment parameters, the patent creates a surface layer that stabilizes the structure for long cycling while maintaining adequate capacity.
Data Source
AI summary
A positive-electrode material for a lithium ion secondary battery contains a lithium complex compound that is represented by the formula: Li1+aNibMncCodTieMfO2+α, and has an atomic ratio Ti3+/Ti4+ between Ti3+ and Ti4+, as determined through X-ray photoelectron spectroscopy, of greater than or equal to 1.5 and less than or equal to 20. In the formula, M is at least one element selected from the group consisting of Mg, Al, Zr, Mo, and Nb, and a, b, c, d, e, f, and a are numbers satisfying −0.1≤a≤0.2, 0.7<b≤0.9, 0≤c<0.3, 0≤d<0.3, 0<e≤0.25, 0≤f<0.3, b+c+d+e+f=1, and −0.2≤α≤0.2.