High-Nickel Cathode Phase Transition Suppression
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Solution Overview
Problem
High-nickel positive active materials in lithium-ion batteries suffer from rapid capacity fading and gas generation due to phase transitions during charge and discharge cycles, limiting their application in high-energy-density devices.
Innovation Solution
A positive active material with a specific composition and structure, including a lithium nickel cobalt manganese oxide formula, is developed to suppress the H2 to H3 phase transition, maintaining cycle stability and reducing gas generation by controlling unit cell parameters and crystal phase changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-nickel positive active materials are used to increase specific capacity, then energy density is improved, but phase transitions occur during charge-discharge cycles causing rapid capacity fading and gas generation
Solution Approach 1:
The patent changes the crystal structure parameter from monoclinic to hexagonal phase, and controls the delithiation percentage parameter t to be in the range of 80-93%, with the 2θ angle difference of the (003) peak not greater than 1.2°. These parameter changes suppress phase transitions during charge-discharge cycles, thereby improving cycle stability while maintaining high specific capacity
Solution Approach 2:
The patent uses composite material strategy by combining multiple elements (Li, Ni, Co, Mn, and other metals) in a specific formula Li l+a Ni x Mn y Co z M l-x-y-z O 2, where -0.05 ≤ a < 0.15, 0.75 < x ≤ 0.95, and y + z < 0.25. This composite material approach creates a stable hexagonal structure that prevents phase transitions and improves both specific capacity and cycle stability
2Use of energy by moving object
If high-nickel positive active materials are used to increase energy density, then specific energy is improved, but gas generation occurs due to phase transitions limiting application
Solution Approach 1:
By changing the crystal structure to hexagonal phase and controlling the delithiation percentage parameter t (80-93%) with the 2θ angle difference of the (003) peak not greater than 1.2°, the patent suppresses phase transitions that cause gas generation. This allows high specific energy to be achieved without the harmful gas generation effect
Solution Approach 2:
The patent converts the potentially harmful phase transition process into a beneficial stable hexagonal structure. By controlling the delithiation percentage and maintaining the hexagonal phase, the material that would normally undergo harmful phase transitions is instead stabilized, converting the harmful phase transition effect into a beneficial stable structure that prevents gas generation
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 solution enhances the electrochemical performance of lithium-ion batteries by improving cycle performance and reducing gas generation, leading to higher capacity retention and stability over multiple charge-discharge cycles.
Implementation Method 1
Based on an initial lithium content of the positive active material, a delithiation percentage of the positive active material is t
Implementation Method 2
a difference between a maximum value and a minimum value of a 2θ angle of a (003) peak of the positive active material in an in-situ X-ray diffraction pattern
Data Source
Figure 1~2
Figure 3~4B
AI summary
A positive active material, wherein, based on an initial lithium content of the positive active material, a delithiation percentage of the positive active material is t, and in a process from a start of delithiation of the positive active material to the delithiation percentage reaching t, a difference between a maximum value and a minimum value of a 2θ angle of a (003) peak of the positive active material in an in-situ X-ray diffraction pattern is not greater than 1.2°,wherein 80% ≤ t ≤ 93%.The electrochemical device that adopts the foregoing positive active material can achieve excellent electrochemical performance, especially reduce gas generation and improve cycle stability of the electrochemical device.