Positive Electrode Active Material Processing via Lithium Borate Removal
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Solution Overview
Problem
Lithium composite transition metal oxides used in secondary batteries face issues with thermal stability and strength, leading to challenges in processing and battery performance due to residual lithium by-products on their surface.
Innovation Solution
A method involving the formation of a lithium borate compound on the surface of lithium transition metal oxides by mixing a boron-containing raw material with the active material precursor and lithium-containing raw material, followed by sintering and subsequent grinding and washing to reduce cake strength and improve processing ease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium composite transition metal oxide is prepared by conventional sintering method, then high capacity and reversible performance are achieved, but residual lithium by-products form on the surface increasing cake strength and causing processing difficulties
Solution Approach 1:
The harmful residual lithium by-products (Li2O, LiOH, Li2CO3) are selectively removed from the cake surface through water washing, extracting the problematic component while preserving the functional lithium composite transition metal oxide particles
Solution Approach 2:
Water is used as an intermediary substance to selectively react with and remove residual lithium by-products from the cake surface during the washing step, facilitating separation without damaging the main product
2Reliability
If LiCoO2 is used as positive electrode active material, then high operating voltage and excellent capacity characteristics are achieved, but poor thermal properties and high cost limit large-scale application
Solution Approach 1:
Lithium composite transition metal oxides with formulas LiM1-x-yM2xM3yO2 or LiM1-x-yM2xM4yO2 are synthesized by combining multiple transition metals (Mn, Ni, Co, Al) to create a composite material that balances high capacity with improved thermal stability and cost-effectiveness
Solution Approach 2:
Different transition metal elements are strategically positioned in the crystal structure to provide local functional properties: Mn for thermal stability, Ni for high capacity, Co for voltage characteristics, and Al for structural stability, achieving overall performance optimization
3Quantity of substance
If LiNiO2 is used to achieve high reversible capacity, then large capacity battery is easily achieved, but poor thermal stability causes decomposition and battery rupture when internal short circuit occurs
Solution Approach 1:
Lithium nickel composite metal oxides with formulas LiM1-x-yM2xM3yO2 or LiM1-x-yM2xM4yO2 are synthesized by combining Ni (for high capacity) with Mn, Co, and/or Al (for thermal stability), creating a composite that balances high reversible capacity with improved thermal safety
Solution Approach 2:
The substitution of部分Ni with thermally stable elements like Mn and Al, which initially reduces pure capacity, actually prevents catastrophic thermal runaway, converting a potential harm (thermal instability) into a benefit (safety) while maintaining acceptable capacity levels
4Strength
If lithium by-products LiOH and Li2CO3 are present on the surface, then they act as adhesive increasing strength between particles, but this increases cake strength causing problems in grinding and sieving
Solution Approach 1:
The adhesive lithium by-products (LiOH and Li2CO3) that cause excessive cake strength are selectively extracted from the particle surfaces through water washing, removing the problematic bonding agent while preserving the main product particles
Solution Approach 2:
Water serves as an intermediary that selectively interacts with and removes the adhesive lithium by-products from particle surfaces during washing, reducing inter-particle bonding strength without damaging the lithium composite transition metal oxide particles
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
This approach enhances the productivity of the positive electrode active material by reducing cake strength and stability issues, leading to improved battery performance and easier processing, while minimizing residual lithium, thus preventing degradation and enhancing the battery's capacity and cycle life.
Implementation Method 1
a boron-containing raw material capable of reacting with residual lithium is added together with a positive electrode active material precursor and a lithium-containing raw material and then sintered
Implementation Method 2
mixing a positive electrode active material precursor having a composition represented by Formula 1 or Formula 2, a lithium-containing raw material, and a boron-containing raw material and sintering the mixture
Implementation Method 3
a second step of preparing a lithium transition metal oxide having the lithium borate compound removed therefrom by grinding the cake
Data Source
AI summary
A method of preparing a positive electrode active material which includes a first step of preparing a cake including a lithium transition metal oxide having a lithium borate compound formed on a surface thereof by mixing a positive electrode active material precursor having a specific composition, a lithium-containing raw material, and a boron-containing raw material and sintering the mixture, and a second step of grinding the cake and washing the ground cake to prepare a lithium transition metal oxide having the lithium borate compound removed therefrom. The method reduces the problems of breaking lithium transition metal oxide during the post processing steps by reduction in cake strength and change in the strength over time, thereby providing a positive electrode active material having improved quality.