Localized Superconcentrated Electrolytes for High-Voltage Li-Ion Cells
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Solution Overview
Problem
Lithium-ion batteries face challenges in extending cycle life, rate capability, energy density, and temperature range due to structural instability of cathode materials and detrimental interactions between cathode and anode materials, particularly at high voltages and temperatures, caused by the poor compatibility of state-of-the-art electrolytes.
Innovation Solution
Development of localized superconcentrated electrolytes (LHCEs) comprising a lithium salt, a nonaqueous solvent, and a diluent, where the lithium salt is soluble in the solvent but insoluble in the diluent, along with an additive, forming localized regions of high salt concentration to enhance stability and compatibility with both anode and cathode materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the charge cut-off voltage is elevated to increase specific capacity and average voltage of NMC cathodes, then energy density is improved, but cathode structural instability and electrolyte decomposition occur at high voltages
Solution Approach 1:
A dual electrolyte system comprising a first electrolyte (LiPF6 in carbonate solvents) and a second electrolyte (LiFSO3 in cyclic carbonate solvents) is employed. The second electrolyte acts as a mediator that forms a stable protective interface on the cathode surface, preventing direct contact between the first electrolyte and the high-voltage cathode material, thereby suppressing decomposition while enabling high voltage operation up to 4.5V vs Li/Li+.
2Use of energy by moving object
If Ni content in NMC cathodes is increased to boost specific capacity, then energy density is improved, but cathode-electrolyte interface stability deteriorates causing continuous electrolyte decomposition
Solution Approach 1:
The second electrolyte (LiFSO3 in cyclic carbonate) serves as an intermediary that preferentially reacts with Ni-rich cathode surfaces to form a stable solid electrolyte interphase (SEI) layer. This protective layer prevents further electrolyte decomposition and transition metal dissolution, enabling stable cycling with high-Ni NMC cathodes at elevated voltages.
Solution Approach 2:
The invention changes the chemical composition parameters of the electrolyte system by introducing LiFSO3 salt and cyclic carbonate solvents with specific molecular structures. This parameter change alters the electrochemical window and interfacial properties, enabling compatibility with high-Ni cathodes that cannot be stabilized by conventional LiPF6-based electrolytes.
3Speed
If state-of-the-art LiPF6-based electrolytes are used to achieve high ionic conductivity, then rate capability is improved, but detrimental interactions with cathode and anode materials occur at high voltages and temperatures
Solution Approach 1:
The dual electrolyte system uses the second electrolyte (LiFSO3/cyclic carbonate) as an intermediary layer between the electrodes and the first electrolyte (LiPF6/carbonate). This intermediary forms stable protective films on both cathode and anode surfaces, preventing harmful interactions while allowing ionic transport, thus maintaining rate capability without sacrificing stability.
Solution Approach 2:
The invention creates a composite electrolyte system combining two different electrolyte formulations (LiPF6-based and LiFSO3-based). Each electrolyte component contributes different properties: the first provides high ionic conductivity, while the second provides interfacial stability. The composite system achieves both high rate capability and enhanced stability against decomposition and metal dissolution.
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 LHCEs improve cycling stability, capacity retention, and Coulombic efficiency, enabling lithium-ion batteries to operate effectively over a wide voltage and temperature range while maintaining stability with nickel-rich cathodes and silicon-based anodes.
Implementation Method 1
a nonaqueous solvent comprising an ester (e.g., a carbonate ester, a carboxylate ester, a phosphate ester, a sulfate ester, or an orthoformate), an ether, a sulfone, a nitrile, or any combination thereof, wherein the lithium salt is soluble in the solvent
Implementation Method 2
a diluent comprising at least one of the following components: a fluoroalkyl ether, a fluorinated orthoformate, a fluorinated carbonate, a fluorinated borate, a fluorinated phosphate, a fluorinated phosphite, or a combination thereof, wherein the lithium salt has a solubility in the diluent at least 10 times less than a solubility of the lithium salt in the solvent
Data Source
AI summary
Electrolytes for lithium ion batteries with carbon-based, silicon-based, or carbon-and silicon-based anodes include a lithium salt; a nonaqueous solvent comprising at least one of the following components: (i) an ester, (ii) a sulfur-containing solvent, (iii) a phosphorus-containing solvent, (iv) an ether, (v) a nitrile, or any combination thereof, wherein the lithium salt is soluble in the solvent; a diluent comprising a fluoroalkyl ether, a fluorinated orthoformate, a fluorinated carbonate, a fluorinated borate, a fluorinated phosphate, a fluorinated phosphite, or any combination thereof, wherein the lithium salt has a solubility in the diluent at least 10 times less than a solubility of the lithium salt in the solvent; and an additive having a different composition than the lithium salt, a different composition than the solvent, and a different composition than the diluent. In some electrolytes, the nonaqueous solvent comprises an ester.