Phosphite Electrolyte for High-Voltage Li-Ion Battery Stability
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Solution Overview
Problem
Lithium-ion batteries face issues with low oxidative stability and high flammability of traditional electrolytes, particularly at high end-of-charge voltages, leading to reduced battery capacity and safety concerns.
Innovation Solution
The development of an electrolyte comprising a lithium salt, specific organic solvents, and a phosphite with a particular formula, which reduces flammability and improves cycling performance by forming a protective layer on the cathode and anode, thereby enhancing the battery's safety and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional carbonate-based electrolytes are used, then high conductivity and good solubility are achieved, but oxidative stability deteriorates and flammability increases
Solution Approach 1:
The phosphite additive performs preliminary action by forming a protective film on the cathode surface before oxidative decomposition can occur. This pre-formed protective layer prevents direct contact between the electrolyte and cathode at high potentials, thereby preventing oxidative decomposition and reducing flammability risks before they can manifest
Solution Approach 2:
The phosphite compound acts as an intermediary substance between the electrolyte and the cathode. It forms a intermediate protective layer (CEI) that mediates the interaction, preventing direct harmful oxidation reactions while allowing ionic transport, thus resolving the contradiction between maintaining electrolyte functionality and preventing oxidative decomposition
2Use of energy by moving object
If end-of-charge voltage is increased above 4.3 V, then energy density is improved, but oxidative decomposition of electrolyte increases
Solution Approach 1:
The phosphite additive performs preliminary protection by forming a stable protective film on the cathode surface before high-voltage operation begins. This pre-formed film acts as a barrier that prevents oxidative decomposition even when the end-of-charge voltage is increased above 4.3 V, enabling high energy density operation without electrolyte degradation
Solution Approach 2:
The invention changes the chemical composition parameter of the electrolyte by introducing phosphite compounds with specific molecular structures (containing P=O or P=S bonds). This parameter change fundamentally alters the electrochemical stability window of the electrolyte, enabling it to withstand higher voltages without decomposition while maintaining ionic conductivity
3Object-affected harmful factors
If phosphite concentration is increased to reduce flammability, then safety is improved, but battery capacity may be affected
Solution Approach 1:
The invention optimizes the concentration parameter of phosphite additive to a specific range (0.1-5 wt.%) where it achieves maximum flammability reduction while maintaining acceptable battery capacity. This precise parameter optimization resolves the contradiction by finding the sweet spot where safety benefits are maximized without excessive capacity loss
Solution Approach 2:
The electrolyte forms a composite system combining traditional carbonate solvents with phosphite additives. This composite electrolyte composition synergistically combines the high conductivity of carbonates with the flame-retardant properties of phosphites, achieving both safety improvement and acceptable performance without requiring excessive phosphite concentrations
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 significant reduction in flammability with lower phosphite concentrations compared to previous compounds, improving cycling behavior and extending battery life, especially at high-voltage applications, while maintaining or exceeding the performance of standard electrolytes.
Implementation Method 1
The role of the additive is to form a protective layer (CEI) on the cathode and thus prevent or reduce the electrolyte decomposition
Implementation Method 2
The flammability of the electrolyte is reduced
Data Source
AI summary
An electrolyte includes at least one lithium salt, at least one first organic solvent having a dielectric constant of >90 at 40° C., at least one second organic solvent having a boiling point of <110° C., and at least one phosphite having the formula (I)R1 is selected from an n-propoxy group, an iso-propoxy group, a tert-butoxy group, an n-pentafluoropropoxy group, an n-trifluoropropoxy group, an iso-hexafluoropropoxy group, or a tert-nonafluorobutoxy group. R2, R3, R4, and R5 are each selected, independently of one another, from H, a trifluoromethyl group, or a C2-C6-alkyl group which is substituted with a trifluoromethyl group.