Graphite Negative Electrode Potential Control in High-Voltage Batteries
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Solution Overview
Problem
Secondary batteries face challenges in achieving superior battery characteristics, particularly in maintaining high energy density and preventing lithium metal precipitation, especially when the charge voltage is increased to 4.38 V or higher, which can lead to capacity loss and gas generation.
Innovation Solution
The secondary battery incorporates a positive electrode with lithium-cobalt composite oxide and a negative electrode with graphite, where the negative electrode's open circuit potential is maintained between 19 mV to 86 mV in a full charge state, and the potential variation is greater than or equal to 1 mV during discharge, ensuring the charge voltage does not exceed the potential constant region associated with phase transition, thereby preventing lithium metal precipitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the charge voltage is increased to 4.38 V or higher to achieve higher energy density, then the battery capacity and energy density are improved, but lithium metal precipitation occurs leading to capacity loss and gas generation
Solution Approach 1:
The patent controls the open circuit potential of the negative electrode within a specific range (19 mV to 86 mV versus lithium reference electrode) and ensures potential variation is at least 1 mV during discharge. These parameter specifications prevent the electrode potential from entering the potential constant region associated with phase transition, thereby suppressing lithium metal precipitation while maintaining high charge voltage of 4.38 V or higher for improved energy density.
2Quantity of substance
If the charge voltage is increased to 4.38 V or higher to achieve higher energy density, then the battery capacity is improved, but capacity loss occurs due to lithium metal precipitation
Solution Approach 1:
By specifying the open circuit potential range (19 mV to 86 mV) and minimum potential variation (1 mV or more), the patent prevents lithium metal precipitation on the negative electrode during high voltage charging. This parameter control ensures that the battery achieves high capacity through increased charge voltage without suffering capacity loss from lithium plating and subsequent decomposition reactions.
Solution Approach 2:
The patent uses open circuit potential measurement as a feedback parameter to monitor and control the negative electrode state. By measuring the open circuit potential versus lithium reference electrode and comparing it against the specified range, the battery design ensures operation conditions that prevent lithium metal precipitation, thereby maintaining capacity integrity during high voltage charging cycles.
3Use of energy by moving object
If the charge voltage is increased to 4.38 V or higher to achieve higher energy density, then the energy storage capability is improved, but gas generation and battery degradation occur
Solution Approach 1:
The patent controls the negative electrode potential parameters (open circuit potential between 19 mV to 86 mV and potential variation of at least 1 mV) to prevent lithium metal precipitation. This suppression of lithium plating eliminates the source of gas generation that would otherwise occur through decomposition reactions of precipitated lithium metal, thereby enabling high energy storage capability at 4.38 V charge voltage without harmful gas evolution.
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 configuration effectively suppresses capacity loss, gas generation, and battery degradation, ensuring stable battery performance even when the charge voltage is increased, thereby achieving superior battery characteristics.
Implementation Method 1
A open circuit potential, versus a lithium reference electrode, of the negative electrode measured in a full charge state is from 19 mV to 86 mV
Implementation Method 2
The secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution
Data Source
AI summary
A secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. The positive electrode includes a lithium-cobalt composite oxide having a layered rock-salt crystal structure. The negative electrode includes graphite. An open circuit potential of the negative electrode measured in a full charge state is from 19 mV to 86 mV. A potential variation of the negative electrode is greater than or equal to 1 mV when the secondary battery is discharged from the full charge state by a capacity corresponding to 1% of a maximum discharge capacity. The maximum discharge capacity is obtained when the secondary battery is discharged with a constant current from the full charge state until the closed circuit voltage reaches 3.00 V, following which the secondary battery is discharged with a constant voltage of the closed circuit voltage of 3.00 V for 24 hours.