Solid-State Polymer Electrolyte for 5V Li-Ion Cells Without Dendrites
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Solution Overview
Problem
Current lithium-ion batteries with solid-state electrolytes (SSEs) exhibit low nominal voltages of approximately 3.2-3.7V per cell and low usable energy densities due to low ionic conductivities, limiting their ability to operate at high voltages above 4.5V, and are prone to thermal runaway and dendrite growth.
Innovation Solution
A high-ionic-conductivity solid-state electrolyte composed of a P(VDF-HFP) polymer matrix, sulfolane plasticizer, lithium salt, and ceramic nanoparticles (Li7La3Zr2O12 derivatives) is developed, enhancing ionic conductivity and mechanical strength, preventing dendrite growth, and enabling safe operation at high voltages up to 5V.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solid-state electrolytes are used to replace organic liquid electrolytes, then safety is improved (non-flammable), but ionic conductivity deteriorates (low ionic conductivities)
Solution Approach 1:
The patent employs a composite solid-state electrolyte consisting of a polymer matrix (P(VDF-HFP)), ceramic nanoparticles (LLZO with Al/Ta/Nb substitutions), and lithium salt. This composite structure combines the safety advantages of solid electrolytes with enhanced ionic conductivity through the synergistic effects of different materials, achieving both non-flammability and high ionic conductivity required for 5V operation.
Solution Approach 2:
The patent modifies the chemical composition and structure of the solid-state electrolyte by substituting Al, Ta, or Nb in Zr sites of Li7La3Zr2O12 ceramic nanoparticles. These parameter changes in the material composition enable higher ionic conductivity while maintaining the solid-state safety advantages, allowing operation at 5V.
2Reliability
If solid-state electrolytes with low ionic conductivity are used, then safety is improved, but energy density deteriorates (low usable energy densities)
Solution Approach 1:
The composite electrolyte system enables high energy density (250-350 Wh/kg) by combining materials that provide both safety and high ionic conductivity, allowing the battery to store and deliver more energy while maintaining solid-state safety advantages.
Solution Approach 2:
By modifying the electrolyte composition with specific ceramic nanoparticle substitutions, the patent achieves the high ionic conductivity necessary to support high energy density operation at 5V, resolving the trade-off between safety and energy density.
3Reliability
If conventional solid-state electrolytes are used, then safety is improved, but voltage capability deteriorates (cannot operate at high voltages above 4.5V)
Solution Approach 1:
The composite electrolyte with substituted LLZO ceramic nanoparticles provides enhanced electrochemical stability and high voltage capability (5V operation) while maintaining the inherent safety advantages of solid-state electrolytes, overcoming the voltage limitation of conventional SSEs.
Solution Approach 2:
The chemical substitution in the ceramic nanoparticle structure modifies the electrolyte's electrochemical properties, enabling it to withstand and operate at high voltages up to 5V while preserving safety characteristics.
4Power
If higher voltage operation is implemented, then power density is improved, but thermal stability deteriorates (thermal runaway risk)
Solution Approach 1:
The composite solid-state electrolyte structure provides inherent thermal stability while enabling high power density operation. The solid-state nature prevents thermal runaway, and the enhanced ionic conductivity supports high discharge rates (up to 5C) at 5V nominal voltage.
Solution Approach 2:
The modified electrolyte composition enhances both thermal stability and ionic conductivity, allowing the battery to achieve high power density (750 W/kg) while maintaining safety and resistance to thermal runaway.
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 electrolyte achieves high energy densities of 250-350 Wh/kg and power densities of 750 W/kg, with safe operation over a wide temperature range, reduced thermal risk, and long service life, suitable for military and portable electronic applications.
Implementation Method 1
high-ionic-conductivity solid-state electrolyte
Implementation Method 2
a P(VDF-HFP) polymer matrix
Implementation Method 3
a plasticizer that comprises sulfolane (SL)
Implementation Method 4
a lithium salt... which provides mobile ions
Implementation Method 5
preventing dendrite growth
Implementation Method 6
During the electrochemical discharge process lithium ions are transported through the electrolyte from the anode to the cathode. As lithium ions are taken up by the cathode, there is a simultaneous release of electrical energy.
Data Source
AI summary
High voltage, high-ionic-conductivity, fire resistant solid-state polymer electrolytes include poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP), sulfolane plasticizer, lithium salt, and ceramic nanoparticles with the basic formula Li7La3Zr2O12 (LLZO) and derivatives thereof. During the curing process, the presence of the LLZO nanoparticles prevent the P(VDF-HFP) from developing into a crystalline phase. In the electrolyte formed, the P(VDF-HFP) is in an amorphous phase with LLZO nanoparticles, lithium salt and sulfolane distributed in the polymer matrix. The solid-state electrolyte with the amorphous polymer phase exhibit higher ionic conductivities than those having a crystalline polymer phase. The LLZO contributes to mechanical properties of the electrolyte and also function as tough ceramic fillers that inhibit lithium dendrite growth during operation of lithium-ion cells and batteries. 5V all-solid-state lithium-ion batteries incorporated the electrolytes exhibit high energy densities (250-350 Whr/kg), high power densities (high discharge rate up to 5 C) and long service lives (500-1500 cycles, <2% irreversible loss/month).