Lithium Ion Battery Electrolyte Flame Retardancy
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Solution Overview
Problem
Lithium ion secondary batteries with nonaqueous electrolyte solutions face challenges in maintaining long-term flame retardancy and capacity retention due to the reductive decomposition of phosphate esters and halogen-substituted compounds, leading to increased resistance and decreased battery performance.
Innovation Solution
A nonaqueous electrolyte solution comprising a lithium salt, an oxo-acid ester derivative of phosphorus, and a disulfonate ester, with specific concentrations and a cyclic carbonate ester containing a halogen, which forms a stable Solid Electrolyte Interface (SEI) to suppress reductive decomposition and enhance flame retardancy and ionic conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phosphate esters are used as electrolyte solvents to achieve high dielectric constant and ionic conductivity, then lithium ion conductivity is improved, but flash point decreases and flame retardancy is poor
Solution Approach 1:
The patent uses a composite electrolyte system combining phosphate ester base solvents with fluorinated cyclic carbonate additives. This composite approach allows the phosphate ester to provide high ionic conductivity while the fluorinated additive forms a protective SEI layer that improves flame retardancy, resolving the contradiction between conductivity and safety
Solution Approach 2:
The fluorinated cyclic carbonate compound acts as an intermediary substance that forms a protective interface layer (SEI) between the electrode and the phosphate ester electrolyte. This intermediary layer prevents direct contact and reduces the flammability risk while maintaining ionic conductivity through the interface
2Object-affected harmful factors
If halogen-substituted phosphate esters are used to improve flame retardancy, then safety is enhanced, but reductive decomposition occurs on carbon negative electrode during long-term usage
Solution Approach 1:
The patent changes the chemical parameters of the cyclic carbonate additive by introducing fluorine atoms at specific positions and controlling the carbon chain length. This parameter optimization allows the additive to form stable SEI films that prevent reductive decomposition of phosphate esters during long-term cycling while maintaining flame retardancy
Solution Approach 2:
The fluorinated cyclic carbonate additive performs preliminary action by forming a stable protective SEI layer on the carbon negative electrode during initial cycles. This pre-formed protective layer prevents subsequent reductive decomposition of the phosphate ester electrolyte during long-term usage, addressing the stability issue before it occurs
3Productivity
If conventional electrolyte solutions are used to achieve initial battery performance, then charge/discharge characteristics are good, but capacity maintenance rate decreases over time due to resistance rise
Solution Approach 1:
The fluorinated cyclic carbonate acts as an intermediary that forms a stable SEI protective layer, mediating between the electrode and electrolyte to prevent harmful reactions over time. This intermediary layer maintains low resistance and prevents capacity fade, improving long-term capacity maintenance while preserving initial charge/discharge performance
Solution Approach 2:
The additive provides beforehand cushioning by forming a protective SEI layer in advance that cushions against the harmful effects of long-term operation. This protective layer prevents resistance rise and capacity degradation over time, ensuring both initial performance and long-term durability
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 solution provides a nonaqueous electrolyte solution with improved long-term flame retardancy and capacity maintenance rate, reducing resistance and gas generation, thereby ensuring high safety and performance over extended periods.
Implementation Method 1
which forms a stable Solid Electrolyte Interface (SEI) to suppress reductive decomposition
Implementation Method 2
suppress reductive decomposition and enhance flame retardancy
Implementation Method 3
these carbonates are likely to have a low flash point and be combustible though having a high dielectric constant and a high ionic conductivity of lithium ions
Implementation Method 4
a nonaqueous electrolyte solution comprising a lithium salt
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(b)
Figure 3
AI summary
The exemplary embodiment has an object to provide a nonaqueous electrolyte solution having a flame retardancy over a long period and having a good capacity maintenance rate. The exemplary embodiment is a nonaqueous electrolyte solution containing a lithium salt, at least one oxo-acid ester derivative of phosphorus selected from compounds represented by a predetermined formula, and at least one disulfonate ester selected from a cyclic disulfonate ester and a linear disulfonate ester represented by the predetermined formulae.