Lithium Ion Battery Voltage Control Preventing Copper Dissolution
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Solution Overview
Problem
Lithium ion secondary batteries using lithium-transition metal composite oxides with an olivine structure face issues with negative electrode current collector dissolution, leading to internal short circuits and reduced service life, especially when used in hybrid vehicles where the battery voltage can approach the dissolution potential during prolonged stops.
Innovation Solution
A control method that sets a lower limit battery voltage within a specific range relative to the positive electrode potential and negative electrode dissolution potential, allowing for controlled charging to prevent the battery voltage from decreasing to the dissolution point, thereby preventing negative electrode potential increase and subsequent current collector dissolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the battery is discharged to maximize energy utilization, then the discharge capacity increases, but the negative electrode potential increases to the dissolution potential causing current collector dissolution
Solution Approach 1:
The patent changes the parameter of lower limit battery voltage from a fixed value to a dynamic value that is adjusted based on the positive electrode potential and state of charge. By setting the lower limit voltage to (B−C+α) V where α is between -0.1 and 0.2, the system prevents the negative electrode potential from reaching the dissolution potential while maximizing discharge capacity utilization.
2Reliability
If the lower limit battery voltage is set high to prevent copper dissolution, then the negative electrode potential is controlled, but the discharge capacity is reduced
Solution Approach 1:
The patent makes the lower limit battery voltage dynamic rather than fixed. The voltage threshold is adjusted based on the positive electrode potential B and state of charge C, allowing the system to optimize between preventing copper dissolution and maximizing discharge capacity under different operating conditions.
Solution Approach 2:
By introducing the parameter α (between -0.1 and 0.2) that adjusts the lower limit voltage relative to (B−C), the system fine-tunes the voltage threshold to prevent copper dissolution while minimizing the impact on discharge capacity. This parameter adjustment allows optimization based on specific battery characteristics and operating conditions.
3Use of energy by moving object
If the battery is used in hybrid vehicles with prolonged stops, then energy efficiency is improved, but the negative electrode potential reaches dissolution potential due to continuous discharge
Solution Approach 1:
The patent implements a feedback mechanism where the lower limit battery voltage is continuously adjusted based on the positive electrode potential B and state of charge C. This feedback control ensures that even during prolonged vehicle stops with continuous discharge for electronic equipment, the negative electrode potential does not reach the dissolution potential, maintaining reliability while allowing energy-efficient operation.
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 prolongs the battery's service life by preventing internal short circuits and maintaining discharge capacity, even as the battery capacity degrades, while allowing continuous operation of electronic equipment during vehicle stops.
Implementation Method 1
a positive electrode having a positive electrode active material that undergoes charge and discharge in a two-phase coexistence state and a negative electrode having a negative electrode active material
Implementation Method 2
The charge and discharge potential remains substantially unchanged even when lithium ions are desorbed or absorbed. This is because the lithium-transition metal composite oxide with an olivine structure enters a two-phase coexistence state of LiFePO4 and FePO4 when Li is absorbed or desorbed.
Implementation Method 3
the negative electrode current collector made of copper (copper foil, or the like) dissolves as the negative electrode potential increases to about 1.2 V. After that, a short circuit (internal short circuit) occurs between the positive and negative electrodes because of precipitation of dissolved copper
Data Source
AI summary
A control method for a lithium ion secondary battery includes performing a charging step of charging the lithium ion secondary battery with a predetermined quantity of electricity when the battery voltage of the lithium ion secondary battery has decreased to a lower limit battery voltage that is set at a value that falls within a range higher than (B−C) V and lower than or equal to (B−C+0.2) V where a maximum value of a positive electrode potential of a flat portion in a discharge positive electrode potential curve is B (V) and a negative electrode dissolution potential is C (V). It is possible to suppress a dissolution of a negative electrode current collector of the lithium ion secondary battery to prevent the service life of the lithium ion secondary battery from shortening because of an internal short circuit.