Lithium Secondary Cell Production Method for Impurity Control
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Solution Overview
Problem
Lithium secondary cells face issues with concentrated precipitation of metal impurities on the negative electrode, leading to short circuits due to inadequate dissolution and diffusion of metal ions during the charging process.
Innovation Solution
A method involving rapid micro-charging and micro-discharging cycles, with short charging and standing times, enhances the dissolution and diffusion of metal impurities, preventing their concentrated precipitation on the negative electrode by maintaining the positive electrode potential above the redox potential and allowing sufficient diffusion time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If repeated micro-charging is performed to dissolve residual alkalis, then residual alkalis are removed from the positive electrode surface, but metal impurities precipitate in a concentrated manner on the negative electrode
Solution Approach 1:
The patent applies periodic charging and discharging cycles instead of continuous charging. By alternately charging and discharging the battery multiple times, the negative electrode potential periodically increases during discharge, preventing continuous concentrated precipitation of metal impurities while still achieving dissolution of residual alkalis during charge phases.
Solution Approach 2:
The patent changes the electrical potential parameter of the negative electrode by switching between charging and discharging modes. During discharge, the negative electrode potential increases to a level that prevents concentrated precipitation, whereas during charge, it decreases to allow dissolution of residual alkalis. This dynamic parameter change resolves the contradiction.
2Stability of the object's composition
If the cell is allowed to stand for a long time after charging to increase negative electrode potential, then dissolved metal ions can diffuse, but concentrated precipitation occurs during long-term charging before discharge
Solution Approach 1:
The patent performs preliminary discharge action immediately after charging to prevent concentrated precipitation from occurring during extended charging periods. By discharging soon after charging, the negative electrode potential is raised before metal impurities can accumulate in concentrated form, while still allowing sufficient diffusion time through the subsequent discharge and standing periods.
3Object-affected harmful factors
If rapid micro-charging and micro-discharging cycles are used to prevent concentrated precipitation, then metal ions are dispersed over a wider area, but the process time increases
Solution Approach 1:
The patent applies a limited number of charging-discharging cycles (typically 1-5 cycles) rather than continuous or excessive cycling. This partial action is sufficient to achieve the dispersion effect and prevent concentrated precipitation, while minimizing the time loss associated with multiple complete charge-discharge cycles. The process stops once the desired dispersion effect is achieved.
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 inhibits the growth of metal impurities towards the positive electrode, reducing the likelihood of short circuits and ensuring the reliability of lithium secondary cells by dispersing metal ions over a wider area on the negative electrode.
Implementation Method 1
charging the assembly within 1 min so that a maximum achieved potential of the positive electrode becomes 3.2 V or more with respect to the redox potential of lithium... the dissolution and diffusion of metal impurities
Implementation Method 2
allowing the assembly to stand for 10 min or less after the charging has ended... enhances the dissolution and diffusion of metal impurities
Implementation Method 3
a negative electrode having a negative electrode active material capable of absorbing and releasing lithium ions
Implementation Method 4
a separator interposed between the positive electrode and negative electrode
Data Source
AI summary
Provided is a method for producing a lithium secondary cell with which the concentrated precipitation of metal impurities at the negative electrode is inhibited and short circuiting is unlikely to occur. The production method includes, assembling together the positive electrode, the separator, and the negative electrode, and then impregnating the assembly with the nonaqueous electrolyte; charging the assembly within 1 min so that a maximum achieved potential of the positive electrode becomes 3.2 V or more with respect to the redox potential of lithium; allowing the assembly to stand for 10 min or less after the charging has ended; and discharging the assembly within 1 min after the standing step.