Lithium Metal Phosphate Washing with Ion-Containing Solution
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Solution Overview
Problem
The discharge capacity of lithium secondary batteries decreases when lithium metal phosphate is washed with water for extended periods, leading to the elution of lithium ions and the formation of a heterogeneous layer that inhibits ion diffusion.
Innovation Solution
A method involving washing lithium metal phosphate with a lithium-ion containing solution, specifically using LiClO4, Li2CO3, LiOH, LiPF6, Li3PO4, or LiH2PO4 in water at a pH of 5 to 9 and a temperature of 15°C or higher for one hour or less, to suppress lithium ion elution and improve discharge rate and charge-discharge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lithium metal phosphate is washed with water for extended periods to remove impurities, then purity increases, but discharge capacity decreases due to lithium ion elution and formation of heterogeneous layer
Solution Approach 1:
A pH buffer solution is introduced as an intermediary washing medium instead of pure water. The buffer solution maintains a controlled pH environment that prevents lithium ion elution while effectively removing impurities, thus resolving the contradiction between purity enhancement and capacity preservation
Solution Approach 2:
The washing process parameters are changed by controlling pH within the range of 4-10 (optimally 6-8) and limiting washing time to 1 hour or less. These parameter adjustments prevent the formation of heterogeneous layers and lithium ion loss while maintaining effective impurity removal
2Manufacturing precision
If washing time is extended to thoroughly remove impurities, then purity improves, but lithium ions are eluted from the surface forming heterogeneous layer that inhibits ion diffusion
Solution Approach 1:
The pH buffer solution acts as an intermediary that enables effective impurity removal within a limited time frame (1 hour or less). The buffered environment maintains washing efficiency without requiring extended exposure times that would cause lithium ion elution
Solution Approach 2:
The washing process uses partial action by limiting the washing time to 1 hour or less, which is sufficient to remove surface impurities but insufficient to cause significant lithium ion elution. The pH buffer enhances the effectiveness of this partial washing action
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 method effectively prevents lithium ion elution during the washing process, enhancing the discharge rate and charge-discharge capacity of lithium secondary batteries by maintaining the lithium ion ratio and improving the battery's performance.
Implementation Method 1
washing the lithium metal phosphate with a washing liquid containing lithium ions... suppresses the elution of lithium ions from the lithium metal phosphate
Data Source
AI summary
The invention provides a method of producing a cathode active material for a lithium secondary battery, whereby it is possible to configure a lithium secondary battery in which the discharge capacity is improved and elution of lithium ions from the lithium metal phosphate is suppressed when washing the lithium metal phosphate after the same was synthesized. The method of producing a cathode active material for a lithium secondary battery includes synthesizing a lithium metal phosphate represented by a composition formula LiMPO4, wherein the element M represents one or two or more of transition metals selected from among Fe, Mn, Co and Ni, and after the synthesis, washing the lithium metal phosphate with a washing liquid containing lithium ion.