Depth-of-Discharge Charging Profiles for Lithium Dendrite Control
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Solution Overview
Problem
Lithium metal deposition in secondary batteries often results in dendrite formation during charging, leading to reduced cycle characteristics and increased side reactions, making it difficult to control the deposition form and prolonging charging time.
Innovation Solution
A charging method that selects between a first and second charging profile based on the depth of discharge (DOD) of the battery, with the first profile having fewer steps and a smaller electric current density for shallow DOD and the second profile having more steps and a larger electric current density for deeper DOD, to balance charging time and cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If small electric current is used during charging to suppress dendritic lithium metal deposition, then dendrite generation is suppressed, but charging time becomes longer
Solution Approach 1:
The charging process is divided into multiple stages with different current densities. The patent applies a first charging step with a first electric current density to form an initial lithium metal layer, followed by a second charging step with a second electric current density (higher than the first) to thicken the lithium metal layer. This segmentation allows the system to achieve both dendrite suppression and reduced charging time by optimizing current density for each stage.
Solution Approach 2:
The charging current density is dynamically adjusted based on the state of the lithium metal layer formation. The patent transitions from a lower current density in the first charging step to a higher current density in the second charging step, making the charging process adaptive to the battery's state. This dynamic adjustment enables the system to maintain dendrite suppression while minimizing charging time.
2Productivity
If multi-stage charging with increased current density is applied, then charging time is reduced, but side reactions between lithium metal and non-aqueous electrolyte increase
Solution Approach 1:
The patent performs a preliminary charging step at a lower electric current density to form an initial lithium metal layer before applying higher current density. This preliminary action creates a stable foundation that reduces subsequent side reactions. By preparing the lithium metal layer in advance with controlled deposition, the system can then safely apply higher currents to reduce charging time without excessive side reactions.
Solution Approach 2:
The patent carefully controls and changes the electric current density parameter between charging stages. The first electric current density is set to a lower value to minimize side reactions during initial lithium metal formation, while the second electric current density is increased to improve charging speed. This parameter optimization balances charging productivity with suppression of harmful side reactions.
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 approach effectively suppresses dendrite growth, shortens charging time, and maintains excellent cycle characteristics by adjusting the charging profile according to the battery's state of charge, thereby improving the practicality and performance of lithium secondary batteries.
Implementation Method 1
during charging, lithium metal deposits in the negative electrode
Implementation Method 2
during discharging, the lithium metal dissolves in the non-aqueous electrolyte
Data Source
AI summary
A method of charging a lithium secondary battery including: a step of charging the lithium secondary battery based on any of a first charging profile and a second charging profile, wherein the first charging profile includes at least two charging steps, the second charging profile includes more charging steps than the first charging profile, at a starting point of the step of charging the secondary battery, the first charging profile is selected when the secondary battery has a depth of discharge of less than a predetermined threshold, and the second charging profile is selected when the secondary battery has a depth of discharge of the threshold or more.