Silicon-Containing Cyclic Compound for High-Voltage Lithium Battery

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Solution Overview

Problem

High-voltage charging and discharging in lithium secondary batteries with positive electrode potentials above 4.2 V lead to transition metal dissolution, causing degradation of cycle characteristics due to deactivated lithium, which existing technologies fail to effectively inhibit.

Innovation Solution

Incorporating a silicon-containing cyclic compound with a vinyl group at the negative electrode, such as a vinyl group-containing cyclic siloxane, to inhibit the degradation of cycle characteristics by reacting with dissolved transition metals, and using a non-aqueous electrolyte with a fluorinated carbonate to prevent oxidative decomposition.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If high-voltage charging and discharging (4.2 V or above) is performed to increase energy density, then power output is improved, but transition metal dissolution occurs leading to degradation of cycle characteristics

Engineering Contradiction:

Improvepower outputVSAvoidcycle characteristics

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

A silicon-containing cyclic compound with a vinyl group is introduced as an intermediary substance in the non-aqueous electrolyte. This compound preferentially reacts with dissolved transition metals to form stable complexes, preventing the transition metals from deactivating lithium. The intermediary substance thus protects the lithium from harmful interactions while allowing high-voltage operation to continue.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The dissolved transition metals, which normally cause harm by deactivating lithium, are converted into beneficial complexes through reaction with the silicon-containing cyclic compound. The compound transforms the harmful dissolved metals into stable, non-deactivating complexes that no longer negatively impact cycle characteristics.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If conventional cyclic siloxanes (e.g., hexamethylcyclotrisiloxane) are added to increase cycle characteristics, then some improvement is achieved, but the effect is insufficient at 4.2 V or higher

Engineering Contradiction:

Improvecycle characteristicsVSAvoidcharging and discharging performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The invention changes the chemical structure parameters of the cyclic siloxane by introducing a vinyl group and replacing methyl groups with smaller substituents. This structural modification enables the compound to effectively complex with transition metals at high voltages (4.2 V or above), providing sufficient cycle characteristic improvement without sacrificing charging and discharging performance.

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If high-voltage operation is maintained to maximize energy density, then battery capacity is improved, but oxidative decomposition of the non-aqueous electrolyte occurs

Engineering Contradiction:

Improvebattery capacityVSAvoidelectrolyte stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The silicon-containing cyclic compound performs preliminary protection by forming a stable complex with dissolved transition metals before these metals can catalyze oxidative decomposition of the electrolyte. This preliminary complexation action prevents the subsequent harmful oxidation reactions, maintaining electrolyte stability during high-voltage operation.

Inventive Principle:

Principle #10Preliminary action

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 silicon-containing cyclic compound significantly enhances cycle characteristics and reduces initial resistance in 4.2 V or higher class lithium secondary batteries, enabling them to maintain performance in high-voltage charging and discharging, suitable for use in vehicles like hybrid and electric vehicles.

Implementation Method 1

the silicon-containing cyclic compound contributes to bring about greater cycle characteristics in a 4.2 V or higher class secondary battery... act to inhibit degradation of cycle characteristics caused by a transition metal dissolved out from the positive electrode active material

Methodology Applied

Scientific EffectComplexation reaction: Chemical Bonding

Implementation Method 2

high-voltage charging and discharging tend to lead to transition metal dissolution from the positive electrode active material... The dissolved transition metal deactivates lithium that contributes to charging and discharging

Methodology Applied

Scientific EffectOxidative decomposition: Oxidation

Data Source

PatentUS9793547B2Lithium secondary battery and method for producing same

Publication Date: 2017.10.17 TOYOTA JIDOSHA KK

AI summary

This invention provides a lithium secondary battery capable of bringing about greater cycle characteristics, being in a 4.2 V or higher class. The lithium secondary battery provided by this invention is a 4.2 V or higher class lithium secondary battery using a lithium transition metal composite oxide as a positive electrode active material. The lithium secondary battery comprises a negative electrode at or around which a silicon-containing cyclic compound and/or a reaction product thereof are present. The silicon-containing cyclic compound comprises at least one silicon atom in its ring and has a vinyl group.