Dual-Electrolyte Refilling for Wide-Range Li-Ion Cell Operation
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Solution Overview
Problem
Lithium-ion batteries with traditional carbonate-based electrolytes are limited by a voltage ceiling of 4.3V and a temperature range of −20° C. to 50° C., due to low ionic conductivity and high charge transfer resistance, which restricts their operational flexibility and long-term calendar life at elevated temperatures.
Innovation Solution
A dual-electrolyte refilling process is employed, where a lithium-ion battery cell is initially filled and formed with a carbonate-based electrolyte to create a lithium fluoride-rich passivation layer, and then flushed with a soft solvents-based electrolyte, comprising methyldifluoroacetate and methyldifluoro(sulfonyl)acetate, to expand the operational voltage and temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If carbonate-based electrolyte is used, then battery can be formed and initial performance is achieved, but operational voltage is limited to 4.3V and temperature range is restricted to −20°C to 50°C
Solution Approach 1:
The electrolyte system is segmented into two distinct phases: (1) carbonate-based electrolyte used during formation to create stable SEI layers, and (2) soft solvent-based electrolyte introduced afterward to enable extended voltage and temperature operation. This segmentation allows each electrolyte type to perform its specialized function without compromising the other.
Solution Approach 2:
The carbonate-based electrolyte is used in advance during the formation process to pre-establish robust SEI layers on electrodes before the battery enters service. This preliminary action creates a protective interface that enables subsequent use of soft solvent electrolytes without direct exposure of electrodes to potentially unstable conditions.
2Adaptability or versatility
If soft solvents-based electrolyte is used directly, then operational voltage and temperature ranges are expanded, but long-term calendar life at elevated temperatures remains unaddressed due to SEI formation issues
Solution Approach 1:
The carbonate-based electrolyte performs the preliminary action of forming stable SEI layers during battery formation before the soft solvent electrolyte is introduced. This pre-formed protective interface prevents direct interaction between soft solvents and electrodes, eliminating long-term degradation issues while retaining the expanded operational range benefits.
Solution Approach 2:
The carbonate-based electrolyte acts as an intermediary during the formation process, mediating between the electrode materials and the subsequent soft solvent electrolyte. It creates a stable interface layer that protects electrodes from direct exposure to soft solvents, enabling long-term stability while allowing soft solvents to provide extended operational range.
3Stability of the object's composition
If carbonate-based electrolyte is used at temperatures below −20°C, then battery structure is maintained, but ionic conductivity decreases and charge transfer resistance increases
Solution Approach 1:
The electrolyte system dynamically changes parameters based on operational conditions: carbonate-based electrolyte provides structural stability during formation, while soft solvent-based electrolyte provides superior low-temperature ionic conductivity and reduced charge transfer resistance during operation, enabling reliable performance across extreme temperature ranges.
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
The method enables lithium-ion batteries to operate at voltages up to 4.5V and temperatures as low as −60° C., while maintaining long-term performance and integrity, by reducing lithium plating and charge transfer resistance through the formation of robust lithium-fluoride interfaces.
Implementation Method 1
saturating the cell's anode, cathode, and separator with a carbonate-based electrolyte to form a lithium fluoride-rich passivation layer between the anode and separator
Implementation Method 2
flushing out the carbonate-based electrolyte with a soft solvents-based electrolyte, leaving the latter within the cell
Implementation Method 3
The soft solvents-based electrolyte within the cell features a mixture of fluorinated esters and ethers, containing dissolved lithium salts such as lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium nitrate
Data Source
AI summary
A lithium-ion battery cell is provided along with a process for its preparation. The method involves first saturating the cell's anode, cathode, and separator with a carbonate-based electrolyte to form a lithium fluoride-rich passivation layer. Subsequently, this electrolyte is flushed and replaced by a soft solvents-based electrolyte. This two-step electrolyte process may help form a more robust initial passivation layer.