NiO-Coated High-Nickel Cathode Material for Residual Lithium Control
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Solution Overview
Problem
Lithium secondary batteries with high nickel content face issues with residual lithium on the surface, leading to oxidation, electrolyte depletion, and deterioration of charging-discharging performance, which affects cycle life and safety, and existing methods to remove residual lithium either damage the surface or fail to sufficiently remove it.
Innovation Solution
A cathode active material with a NiO-like crystalline phase coating of 2.5 nm or less, formed using a weakly acidic or neutral organic buffer during the preparation process, which effectively reduces residual lithium and improves surface stability, comprising a nickel-based lithium transition metal oxide with a layered crystalline phase and a secondary coating layer of cobalt and other metal compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high nickel content is used in the cathode active material to increase capacity, then the battery capacity is improved, but residual lithium remains on the surface causing oxidation and electrolyte depletion
Solution Approach 1:
A coating layer comprising a NiO-like crystalline phase is introduced as an intermediary between the high-nickel cathode active material and the electrolyte. This coating layer acts as a protective barrier that prevents direct contact between the residual lithium on the cathode surface and the electrolyte, thereby eliminating electrolyte depletion while maintaining high battery capacity
Solution Approach 2:
The invention changes the physical and chemical parameters of the cathode surface by forming a specific NiO-like crystalline phase coating with controlled thickness (about 2.5 nm or less). This parameter change transforms the harmful high-nickel surface into a stable, protected interface that prevents oxidation and electrolyte degradation
2Object-affected harmful factors
If existing methods are used to remove residual lithium from the cathode surface, then residual lithium is reduced, but the cathode surface is damaged
Solution Approach 1:
The NiO-like crystalline phase coating is formed preliminarily on the cathode surface before the cathode is assembled into the battery. This preliminary coating action protects the cathode surface from damage during subsequent handling and battery operation, while also preventing residual lithium from causing harm
Solution Approach 2:
Instead of attempting to completely remove residual lithium (which would require harsh treatments that damage the cathode), the invention converts the harmful residual lithium into a beneficial component by forming a NiO-like crystalline phase coating that incorporates the residual lithium. This transforms the problem into a solution, creating a protective layer rather than damaging the surface
3Stability of the object's composition
If a thick coating layer is formed on the cathode surface to protect it, then surface stability is improved, but the initial efficiency and capacity are reduced
Solution Approach 1:
The invention optimizes the thickness parameter of the coating layer to be about 2.5 nm or less. This precise parameter control provides sufficient surface stability and protection while minimizing the blocking effect on lithium ion transport, thereby maintaining high battery capacity and initial efficiency
Solution Approach 2:
The coating layer is applied locally only where needed on the cathode surface, creating a localized protective function. The thin, uniform coating provides surface stability at the interface without significantly affecting the bulk properties and capacity of the cathode active material
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 initial efficiency, capacity, and cycle life of lithium secondary batteries by reducing surface damage and effectively removing residual lithium, thereby improving the overall performance and safety of the batteries.
Implementation Method 1
washing a resulting product of the primary heat treatment using a solvent comprising a weakly acidic or neutral organic buffer
Implementation Method 2
primarily heat-treating a mixture comprising a transition metal precursor and a lithium source
Implementation Method 3
the primary particles comprise a nickel-based lithium transition metal oxide which comprises a layered crystalline phase
Data Source
AI summary
This application relates to a cathode active material for a lithium secondary battery, a method of preparing the cathode active material, a cathode employing the cathode active material, and a lithium secondary battery employing the cathode. The cathode active material may include a secondary particle in which primary particles are aggregated and a first coating layer disposed on the plurality of primary particles to have a thickness of about 2.5 nm or less and including a NiO-like crystalline phase belonging to a Fm3-m space group. The cathode active material may prevent surface deterioration through a washing process using a weakly acidic or neutral organic buffer, thereby improving the initial efficiency characteristic and life characteristics of the lithium secondary battery while maintaining the initial capacity of the lithium secondary battery.