Nonaqueous Electrolyte Composition for Low-Resistance Boron Cathodes
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Solution Overview
Problem
Nonaqueous electrolyte energy storage devices with boron-based additives or boron-coated positive active materials experience a high rate of increase in direct-current resistance after charge-discharge cycles under high temperature.
Innovation Solution
Incorporating a positive composite layer with a transition metal oxide and a boron element, and using a nonaqueous electrolyte containing a sulfuric acid ester compound, with the boron content in the positive composite layer set at 0.03% by mass or more, to form a flexible film that reduces resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a boron-based additive is used in the nonaqueous electrolyte or a boron compound is attached to the surfaces of positive active material particles, then the capacity retention ratio in charge-discharge cycles is improved, but the direct-current resistance increases at a high rate after charge-discharge cycles under high temperature
Solution Approach 1:
The patent changes the chemical composition parameters of the nonaqueous electrolyte by introducing a sulfuric acid ester compound with specific molecular structure (cyclic or chain) and controlled content (0.01-5% by mass). This parameter change modifies the film-forming characteristics and chemical reactivity to reduce DC resistance increase while maintaining capacity retention benefits from boron compounds.
Solution Approach 2:
The patent creates a composite electrolyte system combining boron-based additives (in the positive composite layer) with sulfuric acid ester compounds (in the nonaqueous electrolyte). This composite approach allows the boron compound to form protective films for capacity retention while the sulfuric acid ester compound forms a separate low-resistance interface layer, achieving both benefits simultaneously.
2Reliability
If a boron compound is attached to the surfaces of positive active material particles to suppress electrolyte decomposition, then the positive active material degradation is reduced, but the direct-current resistance increases after charge-discharge cycles under high temperature
Solution Approach 1:
The sulfuric acid ester compound acts as an intermediary substance between the boron-containing positive composite layer and the bulk nonaqueous electrolyte. It forms an intermediate film layer that mediates the interface properties, providing both protection to the positive active material (through boron) and low resistance characteristics (through sulfuric acid ester), thus resolving the contradiction between material stability and electrical conductivity.
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 effectively reduces the rate of increase in direct-current resistance after charge-discharge cycles under high temperature, maintaining capacity retention and improving film flexibility.
Implementation Method 1
a nonaqueous electrolyte containing a sulfuric acid ester compound... form a low-resistance film that flexibly adapts to the positive composite layer's expansion and contraction
Implementation Method 2
modifying the surfaces of positive active material particles is proposed for suppressing the decomposition of the nonaqueous electrolyte on the positive electrode
Data Source
AI summary
An aspect of the present invention is a nonaqueous electrolyte energy storage device including: a positive electrode including a positive composite layer containing a transition metal oxide and a boron element; a negative electrode; and a nonaqueous electrolyte containing a sulfuric acid ester compound, in which the content of the boron element in the positive composite layer is 0.03% by mass or more.