Multi-Step Charging Method for Non-Aqueous Electrolyte Secondary Battery
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Solution Overview
Problem
Existing lithium-ion secondary battery charging methods fail to shorten charging time without deteriorating cycle characteristics, as increasing packing density or reducing charge current leads to either overcharging or reduced discharge capacity.
Innovation Solution
A charging method involving multiple steps of constant-current and constant-voltage charging, where the charge current is adjusted based on the frequency of use and number of charge/discharge cycles, allowing high-rate charging in low-voltage areas and low-rate charging in high-voltage areas, thereby optimizing charge current settings to minimize internal resistance and maintain cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the charge current is decreased to prevent deterioration in cycle characteristics, then the cycle characteristics are improved, but the charging time increases
Solution Approach 1:
The charging process is divided into multiple steps with different charge current values. The method performs constant-current charging at a first charge current value until the battery voltage reaches a first upper limit voltage, then performs constant-current charging at a second charge current value (smaller than the first) until the battery voltage reaches a second upper limit voltage (higher than the first). This segmentation allows high-rate charging in low-voltage areas and low-rate charging in high-voltage areas, resolving the contradiction between charging speed and cycle life.
Solution Approach 2:
The charge current value is dynamically adjusted based on the battery voltage level. The system switches between different charge current values (Ic(1), Ic(2), etc.) and corresponding upper limit voltages (Ec(1), Ec(2), etc.) during the charging process. This dynamic adjustment optimizes both charging efficiency and battery longevity by matching charge rate to battery state.
2Reliability
If the upper limit of charge voltage is lowered to prevent decomposition of non-aqueous electrolyte, then the cycle characteristics are improved, but the discharge capacity decreases
Solution Approach 1:
The charging voltage range is segmented into multiple stages, each with its own upper limit voltage. The first stage uses a lower upper limit voltage (Ec(1)) to prevent electrolyte decomposition, while the second stage uses a higher upper limit voltage (Ec(2) > Ec(1)) to maximize discharge capacity. This segmented approach resolves the contradiction by applying different voltage constraints at different charging stages.
Solution Approach 2:
Different voltage constraints are applied locally to different stages of the charging process. The lower voltage constraint (Ec(1)) is applied during the first constant-current charging stage when the battery voltage is low, and the higher voltage constraint (Ec(2)) is applied during the second constant-current charging stage when the battery voltage is higher. This local quality approach optimizes both electrolyte protection and capacity utilization.
3Quantity of substance
If the packing density of active material is increased to achieve higher capacity, then the capacity is improved, but the lithium ion-acceptability degrades during charging
Solution Approach 1:
The charging current is dynamically adjusted based on the battery voltage and the degraded lithium ion-acceptability caused by high packing density. By switching between different charge current values (Ic(1), Ic(2), etc.) at different voltage stages, the system adapts to the reduced ion acceptance and prevents overcharging, thereby maintaining cycle characteristics despite high capacity.
Data Source
AI summary
Disclosed is a charging method for one or more non-aqueous electrolyte secondary batteries by n steps of constant-current charging processes, where n is an integer equal to or greater than 2. The n steps include: (1) charging the secondary batteries at a current Ic(k) until a charge voltage per one battery reaches a voltage Ec(k), where k is an integer equal to or greater than 1 and equal to or smaller than n−1; and (2) when the charge voltage per one battery reaches the voltage Ec(k), charging the secondary batteries at a current Ic(k+1) smaller than the current Ic(k) until the charge voltage per one battery reaches a voltage Ec(k+1) higher than the voltage Ec(k), in which (3) the currents Ic(k) and Ic(k+1) are set according to frequency of use or number of charge and discharge cycles of the secondary batteries.