SiOx Battery State Estimation via dQ/dV Analysis
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Solution Overview
Problem
Energy storage devices with silicon oxide (SiOx) negative electrodes face challenges in estimating internal states due to changes in capacity balance and cycle performance, as they transition from positive-electrode limiting to negative-electrode limiting types, requiring new methods to assess deterioration and remaining life.
Innovation Solution
An estimation apparatus and method that acquires voltage and energization data to estimate the internal state of energy storage devices with SiOx negative electrodes, using dQ/dV values within specific voltage ranges to determine the transition type and predict capacity degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-doping treatment with Li is performed to construct a positive-electrode limiting type energy storage device, then cycle performance is improved and capacity deterioration is reduced, but the discharge capacity ratio of the negative electrode to the positive electrode increases, leading to reduced utilization factor of the negative electrode
Solution Approach 1:
The patent applies pre-doping treatment with Li ions before battery assembly to intentionally create a positive-electrode limiting type configuration. This preliminary action establishes the desired capacity balance before the battery enters service, preventing premature negative-electrode limiting conditions and improving cycle performance from the outset.
Solution Approach 2:
The patent changes the chemical composition parameters of the negative electrode by controlling the SiOx content and pre-doping Li ion concentration. By adjusting these parameters, the initial capacity ratio between electrodes is optimized to maintain positive-electrode limiting conditions for extended cycle life.
2Quantity of substance
If the energy storage device operates as a negative-electrode limiting type, then the discharge capacity is limited by the negative electrode, but the amount of SEI coating formed on the negative electrode interface increases due to repeated charge and discharge, trapping more Li ions
Solution Approach 1:
The patent applies preliminary pre-doping with excess Li ions to counteract the future loss of Li ions to SEI coating formation. This anticipatory compensation ensures that even as Li ions are trapped in the growing SEI layer, sufficient Li remains available to maintain the positive-electrode limiting condition and prevent transition to negative-electrode limiting operation.
Solution Approach 2:
The patent cushions against the harmful effect of SEI coating by pre-loading the negative electrode with additional Li ions. This creates a buffer that absorbs the Li loss over cycles, maintaining the intended electrode capacity balance and preventing the detrimental transition to negative-electrode limiting behavior.
3Adaptability or versatility
If conventional deterioration estimation methods are used, then they work for typical carbon-based negative electrodes, but they cannot be applied to lithium ion secondary batteries using SiOx for the negative electrode due to differences in characteristics
Solution Approach 1:
The patent identifies and utilizes specific local characteristics of SiOx-based negative electrodes, particularly the unique dQ/dV profile features that emerge during discharge. By focusing on these localized voltage-range-specific properties rather than applying generic estimation methods, accurate deterioration assessment becomes possible for this specific electrode material type.
Solution Approach 2:
The patent employs feedback from measured dQ/dV values during discharge to continuously assess the deterioration state. By monitoring changes in the discharge curve characteristics and comparing them against reference profiles, the system adapts its estimation to account for the specific degradation mechanisms of SiOx-based electrodes.
Data Source
AI summary
An estimation apparatus estimates an internal state of an energy storage device having a positive electrode, a negative electrode including a negative active material that contains SiOx, and a nonaqueous electrolyte, the energy storage device changing from a positive-electrode limiting type, in which a discharge capacity is limited by the positive electrode, to a negative-electrode limiting type, in which the discharge capacity is limited by the negative electrode. The estimation apparatus estimates the internal state of the energy storage device by using a voltage value and an energization amount in a predetermined voltage range of the energy storage device or at a predetermined measured voltage value, or based on information on the shape of a discharge curve of the energy storage device.