Silicon Negative Electrode Cycle Stability via Diisocyanate Additive
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries using particulate silicon or silicon alloy as negative electrode active material face significant capacity degradation and poor charge-discharge cycle performance, especially under high temperature environments, due to reactions with the non-aqueous electrolyte and expansion issues.
Innovation Solution
Incorporating a negative electrode with particulate silicon or silicon alloy and a binding agent, along with fluorinated cyclic carbonate and a diisocyanate compound in the non-aqueous electrolyte, to restrict reactions and enhance adhesion, thereby improving cycle performance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If particulate silicon or silicon alloy is used as negative electrode active material to increase battery capacity, then battery capacity is improved, but charge-discharge cycle performance deteriorates due to reactions with non-aqueous electrolyte and expansion issues
Solution Approach 1:
A diisocyanate compound is introduced as an intermediary substance in the non-aqueous electrolyte. This compound mediates between the silicon-based negative electrode and the electrolyte, suppressing harmful reactions while allowing lithium ion insertion/extraction. The diisocyanate compound forms a protective interface that prevents direct contact between the reactive silicon and electrolyte, thereby improving cycle performance without sacrificing capacity.
Solution Approach 2:
The invention changes the chemical composition parameters of the non-aqueous electrolyte by adding a diisocyanate compound with specific molecular structure (formula 1). This parameter change modifies the electrolyte's interaction properties with the silicon electrode, reducing expansion and reaction effects. The specific structural parameters of the diisocyanate compound (aliphatic or aromatic hydrocarbon groups with specific chain lengths) are optimized to achieve the desired protective effect.
2Quantity of substance
If silicon or silicon alloy is used as negative electrode active material, then theoretical capacity increases to about 4000 mAh/g, but volume change and deterioration from expansion during charging and discharging occur
Solution Approach 1:
The diisocyanate compound acts as a buffering intermediary between the silicon electrode and the external environment. During charging and discharging, this intermediary substance absorbs and mitigates the volume expansion forces, preventing direct mechanical stress on the silicon structure. This allows the silicon to achieve high capacity while maintaining compositional stability.
Solution Approach 2:
The diisocyanate compound provides beforehand cushioning by forming a protective layer on the silicon electrode surface before significant expansion occurs. This pre-formed protective interface cushions against the expansion forces during subsequent charging cycles, preventing structural deterioration and maintaining volume stability.
3Quantity of substance
If silicon or silicon alloy is used as negative electrode active material, then high capacity is achieved, but reaction with commonly used non-aqueous electrolyte causes deterioration
Solution Approach 1:
The diisocyanate compound serves as a chemical intermediary that separates the reactive silicon from the non-aqueous electrolyte. It forms a stable interface layer that prevents direct harmful reactions while still permitting lithium ion transport. This intermediary layer eliminates the harmful reaction products that would otherwise degrade the electrode and reduce capacity.
Solution Approach 2:
The invention converts the harmful reactivity of silicon with electrolyte into a beneficial protective effect. The diisocyanate compound initially interacts with the silicon surface, forming a stable passivation layer that prevents further harmful reactions. This converts the potentially harmful silicon-electrolyte reactivity into a protective mechanism that preserves capacity over multiple cycles.
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 restricts the reaction between the negative electrode and non-aqueous electrolyte, leading to improved charge-discharge cycle performance and stability, even under high temperature conditions, by maintaining a low utilization rate of the negative electrode and preventing excessive expansion and contraction.
Implementation Method 1
charging and discharging by way of transfer of lithium ions between a positive electrode and a negative electrode
Implementation Method 2
a resistance component is formed by the diisocyanate compound of the general formula (1) on the surface of the negative electrode
Implementation Method 3
charging and discharging is performed by insertion and de-insertion of lithium ions among graphite crystals
Data Source
AI summary
The present invention is made to improve charge-discharge cycle performances under high temperature environment in a non-aqueous electrolyte secondary battery using a negative electrode containing a negative electrode active material of particulate silicon and/or silicon alloy and a binding agent.A non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode 11, a negative electrode 12, a separator 13, and a non-aqueous electrolyte, wherein the negative electrode includes a negative electrode active material containing particulate silicon and/or silicon alloy and a binding agent, and the non-aqueous electrolyte contains fluorinated cyclic carbonate and a prescribed diisocyanate compound, and when Li storage volume per unit area of the negative electrode of the non-aqueous electrolyte secondary battery under charging condition is determined as A and the theoretical maximum Li storage volume per unit area of the negative electrode is determined as B, a utilizing rate (%) of negative electrode which is expressed by (A/B)×100 is 45% or less.