Wide Temperature Range Electrolytes for Lithium-Ion Capacitors
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Solution Overview
Problem
Lithium-ion capacitors (LICs) face limitations in energy density and low-temperature performance, with conventional electrolytes unable to discharge effectively at temperatures as low as −40°C, and existing research has not adequately addressed the need for wide operating temperature range electrolytes.
Innovation Solution
Development of two electrolyte formulations, L1 and L2, containing 1M LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + methyl butyrate (MB) with lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFOB) additives, respectively, which enable LICs to operate at temperatures from 70°C to −40°C with improved discharge capacity and cycling performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional electrolytes are used in LICs, then the device can operate at standard temperatures, but it cannot discharge effectively at low temperatures as low as −40°C
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by incorporating specific additives (LiBOB and LiDFOB) at optimized concentrations (0.05-0.2M) into the EC-EMC-MB solvent system. This parameter modification enables the electrolyte to maintain adequate ionic conductivity and discharge capacity across an extended temperature range from 70°C to −40°C, directly resolving the temperature-operability contradiction
Solution Approach 2:
The patent creates a composite electrolyte system by combining multiple components: EC-EMC-MB solvent mixture (20:20:60 v/v%) with lithium salts (LiPF6 at 1M and additives LiBOB/LiDFOB at 0.1M). This composite formulation synergistically improves both the low-temperature discharge performance and high-temperature stability, achieving reliable operation across extreme temperature conditions
2Reliability
If electrolyte additives are added to improve low-temperature performance, then the discharge capacity at −40°C is improved, but the device complexity increases
Solution Approach 1:
The patent applies local quality by introducing specific functional additives (LiBOB or LiDFOB) at precisely controlled low concentrations (0.05-0.2M, optimally 0.1M) into the electrolyte formulation. These localized chemical modifications target specifically the low-temperature ionic conductivity and discharge capacity without fundamentally altering the entire electrolyte system, thus improving reliability while minimizing complexity increase
Solution Approach 2:
The patent uses partial action by adding relatively small amounts of lithium salt additives (0.05-0.2M compared to the main 1M LiPF6) to achieve significant improvements in low-temperature performance. This partial modification approach provides the necessary performance enhancement without requiring complete reformulation of the electrolyte system, thereby limiting the increase in device complexity
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
L2 formulation achieves over 64% discharge capacity retention at −40°C and maintains 96% capacity after 3500 cycles, outperforming L1 and conventional electrolytes, demonstrating superior performance in extreme temperatures.
Implementation Method 1
1M LiPF6 in ethylene carbonate (EC)+ethyl methyl carbonate (EMC)+methyl butyrate (MB) at a ratio of 20:20:60 v/v %, respectively, +0.1M lithium bis(oxalato)borate (LiBOB)
Implementation Method 2
1M LiPF6 in EC+EMC+MB at a ratio of 20:20:60 v/v %, respectively, +0.1M lithium difluoro(oxalato)borate (LiDFOB)
Implementation Method 3
lithium bis(oxalato)borate (LiBOB), and a second electrolyte formulation L2 that was 1M LiPF6 in EC+EMC+MB at a ratio of 20:20:60 v/v %, respectively, +0.1M lithium difluoro(oxalato)borate (LiDFOB), which formulation enabled the LICs to discharge at the temperature as low as −40° C., achieve improved cycling performance and capacity retention after 10,000 cycles
Data Source
AI summary
The present invention provides for two types of wide operating temperature range electrolyte formulations that contain methyl butyrate (MB) and additives have been investigated and compared in Lithium-ion capacitors (LICs), which were consisted of hard carbon (HC)/stabilized lithium metal powder (SLMP) anodes and activated carbon (AC) cathodes. The electrolyte L1 that was 1M LiPF6 in ethylene carbonate (EC)+ethyl methyl carbonate (EMC)+MB (20:20:60 v/v %)+0.1M lithium bis(oxalato)borate (LiBOB) and electrolyte L2 that was 1M LiPF6 in EC+EMC+MB (20:20:60 v/v %)+0.1M lithium difluoro(oxalato)borate (LiDFOB) enabled the LICs to discharge at the temperature as low as −40° C., which the conventional electrolyte LP30 that was 1 M LiPF6 in EC+dimethyl carbonate (DMC) (50:50 w/w %) could not achieve. At the low temperature of −40° C., L2 held more than 64% of the discharge capacity at 30° C., while the L1 only had the discharge capacity retention of 30%. In addition, L2 proved to achieve better cycling performance compared to L1. After 10,000 cycles, the capacity retention of L1 and L2 were about 86.6% and 84.7%, which demonstrated the stable cycling performance for electrolyte L1 and L2. In summary, L2 was the most suitable electrolyte for the LICs energy storage devices which would be applied in the temperature as low as −40° C.