Li-Ni Composite Cathode Stabilizing Lattice Constants
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Solution Overview
Problem
Lithium nickel oxide batteries face challenges with thermal stability, cycle durability, and high discharge capacity due to structural instability and Yantra strain, which existing methods like adding Co and Al or incorporating B and P do not adequately address, leading to reduced capacity and increased side reactions.
Innovation Solution
A Li—Ni composite oxide with a specific chemical composition and dopant content, represented by Chemical Formula 1, stabilizes the crystal structure, controls Ni2+ incorporation, and optimizes the lattice constants of the a-axis and c-axis, incorporating Al, Ti, and Mg as dopants to enhance discharge capacity and cycle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LiNiO2 is used as cathode active material to achieve high charge and discharge capacity, then the battery has high energy density, but the thermal stability and cycle durability deteriorate due to crystal structure instability and Jahn-Teller strain
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core region contains LiNiO2 particles with high capacity, while the outer shell region contains LiNi1-x-yCoxMnyO3-d particles with improved structural stability. This spatial differentiation allows the high-capacity core to function while the stable shell protects it from degradation, resolving the contradiction between capacity and reliability.
Solution Approach 2:
The patent uses composite materials by combining LiNiO2 with LiNi1-x-yCoxMnymO3-d to form a core-shell composite structure. The composite integrates the high capacity advantage of LiNiO2 with the thermal and structural stability of the doped Li-Ni composite oxide, simultaneously achieving both high charge/discharge capacity and improved thermal stability and cycle durability.
2Reliability
If Co and Al are added to Ni in LiNiO2 to stabilize crystal structure, then cycle characteristics improve, but the amount of Ni is significantly reduced requiring higher charging voltage and additional surface treatment
Solution Approach 1:
The patent applies parameter changes by precisely controlling the doping ratios of Co and Mn (where x and y are each independently 0.01 to 0.20, and x+y≤0.30) and the particle size (0.1 to 10 μm). By optimizing these parameters, the patent achieves improved cycle characteristics while avoiding the need for significantly higher charging voltages and reducing the requirement for additional surface treatment processes.
Solution Approach 2:
The patent uses partial action by substituting only a limited portion of Ni with Co and Mn (controlling the substitution ratio through parameters x and y), rather than significantly replacing Ni. This partial substitution is sufficient to stabilize the crystal structure and improve cycle characteristics while maintaining high capacity and avoiding the need for higher charging voltages.
3Reliability
If Li removal treatment is performed to improve cycle and thermal stability, then storage characteristics improve, but the specific surface area increases promoting side reactions with electrolyte at high temperature
Solution Approach 1:
The patent applies preliminary action by performing Li removal treatment during the firing process itself, rather than as a separate post-treatment step. The Li removal is conducted in-situ at high temperature (900 to 1200°C) in an oxygen atmosphere, which simultaneously improves storage characteristics and stabilizes the crystal structure before the material is used in the battery, thereby reducing subsequent side reactions with the electrolyte.
Solution Approach 2:
The patent uses strong oxidants by conducting the Li removal treatment in an oxygen atmosphere at high temperature. The oxygen environment facilitates the oxidation and removal of excess Li from the crystal structure, improving storage characteristics and thermal stability while the controlled conditions prevent excessive surface area increase that would promote side reactions.
4Temperature
If B and P element oxides are incorporated to control crystallite size and improve thermal stability, then thermal stability improves, but the capacity is reduced due to confusion of crystal structure
Solution Approach 1:
The patent applies this principle by using Co and Mn dopants as alternative 'short-living' stabilizing elements that achieve thermal stability without the structural confusion caused by B and P. The Co and Mn dopants provide the necessary structural stabilization while maintaining electrochemical activity, effectively replacing the problematic B and P elements that compromised capacity.
Data Source
AI summary
The present invention relates to a cathode active material, and a lithium secondary battery comprising the same, the present invention provides a cathode active material, represented by the following Chemical Formula 1, wherein I003/I104 ratio is 1.6 or more, and R-factor value represented by the following Formula 1 is 0.40 to 0.44, and c-axis lattice constant (c) and a-axis lattice constant (a) satisfy 3(a)+5.555≤(c)≤3(a)+5.580:R-factor=(I102+I006)/(I101) Formula 1wherein I003, I006, I101, I102, and I104 are the intensity of diffraction peaks on the (003), (006), (101), (102), and (104) planes by X-ray diffraction analysis using CuKα-rays,Liα[(NixCoy)1-βAβ]Oz Chemical Formula 1in the Chemical Formula 1, 0.95≤α≤1.1, 0.75≤x≤0.95, 0.03≤y≤0.25, 0<β≤0.2, and 1.9≤z≤2.1, and A is a dopant metal element, and the average oxidation number N of A is 3.05≤N≤3.35.