Positive Electrode Active Material Washing for LiOH and Li2CO3 Control
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Solution Overview
Problem
Existing methods struggle to effectively adjust and selectively remove lithium by-products (LiOH and Li2CO3) from positive electrode active materials, leading to issues such as gelation of electrode slurry, moisture generation, and poor thermal stability in lithium secondary batteries.
Innovation Solution
A method involving the use of a weak acid to adjust the pH of a lithium composite transition metal oxide to 7 to 10 during washing, allowing for the selective removal of LiOH and Li2CO3, with a molar ratio of 1:1.8 to 1:3, to maintain optimal battery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If water washing is used to remove lithium by-products, then LiOH and Li2CO3 can be removed, but it is difficult to selectively remove LiOH and Li2CO3 and control their residual amounts
Solution Approach 1:
The patent applies parameter changes by adjusting the pH value of the washing solution to 8.0 or higher, which creates selective solubility conditions for different lithium by-products. At this specific pH range, LiOH is preferentially removed while Li2CO3 remains partially retained, achieving both selectivity and precise control of residual by-product amounts. This resolves the contradiction by transforming the washing process from non-selective to selective through pH parameter optimization.
2Reliability
If all lithium by-products are removed, then battery performance improves, but side reactions and corrosion of the NCM-based lithium oxide surface occur
Solution Approach 1:
The patent applies partial action by intentionally leaving a controlled amount of lithium by-products (specifically maintaining Li2CO3 at 0.01-5 wt% and LiOH at 0.01-2 wt%) on the NCM-based lithium oxide surface rather than complete removal. This partial retention prevents surface corrosion and side reactions while still achieving sufficient removal of harmful by-products to maintain good battery performance, thus resolving the contradiction between complete purification and surface protection.
3Object-affected harmful factors
If LiOH and Li2CO3 remain on the surface, then surface corrosion is prevented, but gas generation and pH increase occur affecting battery performance
Solution Approach 1:
The patent applies parameter changes by precisely controlling the pH of the washing solution to 8.0 or higher, which fundamentally alters the solubility and reactivity characteristics of lithium by-products. At this elevated pH, LiOH becomes highly soluble and is preferentially removed, while Li2CO3 maintains lower solubility and is retained in controlled amounts. This parameter transformation resolves the contradiction by converting the harmful presence of LiOH into a removable form while preserving beneficial Li2CO3.
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 method effectively adjusts the washing amount of lithium by-products, improving the capacity and lifetime characteristics of lithium secondary batteries by inhibiting gas generation and corrosion, thereby enhancing battery performance.
Implementation Method 1
adding a weak acid to the water to which the lithium composite transition metal oxide is put to adjust the pH to 7 to 10
Implementation Method 2
selectively remove LiOH and Li2CO3
Data Source
AI summary
A positive electrode active material includes a lithium composite transition metal oxide and a lithium by-product present on the surface of the lithium composite transition metal oxide. The lithium by-product is included at 0.3 mol % to 0.41 mol % with respect to a total mole number of the lithium composite transition metal oxide, and Li2CO3 and LiOH are included at a molar ratio of 1:1.8 to 1:3. A positive electrode including the positive electrode active material and a lithium secondary battery including the positive electrode are also provided.