Ti-Graded Lithium Cobaltate for Battery Cycle Life
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium secondary batteries using lithium cobaltate face degradation in cycle characteristics due to cobalt atom elution, and existing solutions with titanium on the surface of lithium cobaltate composite oxides fail to achieve excellent cycle and rate characteristics while minimizing direct current resistance and gas-related swelling.
Innovation Solution
A lithium-transition metal composite oxide with a specific Ti concentration distribution, produced by mixing lithium, cobalt, and titanium dioxide, where Ti atoms are present both on the surface and within the particles with a concentration gradient, is used as the positive electrode active material, optimizing the molar ratios and firing conditions to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If titanium oxide is coated on the surface of lithium cobaltate particles, then cobalt atom elution is suppressed, but cycle characteristics and rate characteristics deteriorate due to high DC resistance
Solution Approach 1:
The patent applies local quality by creating a non-uniform Ti concentration distribution within the particles. The surface region contains higher Ti concentration (0.03-0.10 atomic ratio) to suppress cobalt elution, while the inner region contains lower Ti concentration (0.003-0.01 atomic ratio) to maintain electrical conductivity. This spatial variation in composition resolves the contradiction between surface protection and bulk conductivity.
Solution Approach 2:
The patent creates a composite structure where lithium cobaltate particles are combined with titanium in a specific concentration gradient. This composite material approach allows the surface to exhibit protective characteristics (high Ti content) while the interior maintains conductive characteristics (low Ti content), achieving both corrosion resistance and electrical performance.
2Reliability
If high concentration of Ti atoms is present on the surface of lithium cobaltate particles, then cobalt elution is suppressed, but rate characteristics and cycle characteristics fail to improve sufficiently
Solution Approach 1:
The patent implements local quality by establishing different Ti concentrations in different regions of the particles. The surface layer (0.03-0.10 atomic ratio Ti) provides corrosion protection, while the interior (0.003-0.01 atomic ratio Ti) ensures rapid electron transport. This local differentiation enables both reliability and speed requirements to be met simultaneously.
Solution Approach 2:
The patent applies parameter changes by varying the Ti concentration parameter spatially within the particles. By controlling the Ti atomic ratio to decrease from surface to interior, the material achieves optimal balance between protective function (surface) and conductive function (interior), resolving the contradiction between cycle life and rate performance.
3Stability of the object's composition
If titanium oxide coating is applied to lithium cobaltate, then particle stability is improved, but gas generation and swelling increase
Solution Approach 1:
The patent uses local quality by concentrating Ti atoms preferentially at the particle surface where they can stabilize the structure and prevent cobalt elution, while minimizing Ti content in the interior to reduce gas-generating side reactions. The surface-enriched Ti distribution provides stability without excessive gas generation.
Solution Approach 2:
The patent creates a Ti concentration profile that copies the functional requirements: high Ti concentration at the surface to provide protective functions, and low Ti concentration in the interior to minimize harmful effects. This graded copying of composition matches the functional needs of different regions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The approach results in lithium secondary batteries with improved cycle and rate characteristics, reduced direct current resistance, and suppressed swelling from gas reactions, while allowing for industrially advantageous production methods.
Implementation Method 1
a part of the surface of the particles of lithium cobaltate is coated with titanium oxide and/or lithium titanate
Implementation Method 2
mixing a lithium compound, a cobalt compound and titanium dioxide and then firing the resulting mixture
Data Source
AI summary
[Problem to be Solved]There can be provided a lithium secondary battery which, when used as a positive electrode active material for lithium secondary batteries, is particularly excellent in cycle characteristics and rate characteristics and low in direct current (DC) resistance and in which the swelling resulting from the generation of gas accompanying the reaction with a nonaqueous electrolyte solution is suppressed. There is also provided a positive electrode active material for lithium secondary batteries in which the positive electrode active material can be industrially advantageously produced.[Solution]The positive electrode active material for lithium secondary batteries according to the present invention includes a lithium-transition metal composite oxide containing from 0.20 to 2.00% by weight of Ti atoms, which is produced by mixing a lithium compound, a cobalt compound and titanium dioxide and then firing the resulting mixture, wherein the Ti atoms are present in the depth direction from the surface of the particles of the lithium-transition metal composite oxide and have a concentration gradient that is highest at the surface of the particles.