Aqueous Battery Electrolyte pH Control for Safety and Energy Density

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Solution Overview

Problem

Nonaqueous lithium secondary batteries face safety concerns due to flammability of organic solvents and high internal resistance, which increases production costs and defects in electric vehicles and stationary energy storage systems, while aqueous solutions struggle with electrolysis and low energy density.

Innovation Solution

A secondary battery design using an aqueous electrolyte with an organic compound containing a carboxyl or carboxylate group and a hydroxyl group, maintaining a pH of 0 or less, which promotes ionization and forms a solid electrolyte interface to enhance charge-discharge properties and cycle life.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If an organic solvent electrolyte solution is used to achieve high electromotive force (2-4.5V), then the energy density is improved, but the safety deteriorates due to flammability

Engineering Contradiction:

Improveenergy densityVSAvoidsafety

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent changes the fundamental parameter of the electrolyte from organic solvent-based to aqueous-based, while adjusting the pH to 0 or less to prevent water electrolysis. This parameter change allows the system to achieve both safety (non-flammable) and acceptable energy density by using lithium manganese oxide and lithium vanadium oxide electrode materials with appropriate potential ranges.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite electrolyte system combining aqueous solution with specific pH control mechanisms and complementary electrode materials (lithium manganese oxide and lithium vanadium oxide). This composite approach enables the system to overcome the limitations of pure aqueous electrolytes while maintaining safety advantages.

Inventive Principle:

Principle #40Composite materials

2Reliability

If an aqueous electrolyte solution is used to improve safety, then the flammability risk is reduced, but the energy density deteriorates due to limited potential range

Engineering Contradiction:

ImprovesafetyVSAvoidenergy density

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent adjusts the pH parameter to 0 or less, which fundamentally changes the electrochemical stability window of the aqueous electrolyte. This parameter change prevents water electrolysis and enables the use of electrode materials with higher potential differences, thereby increasing energy density while maintaining safety.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a localized acidic environment (pH 0 or less) within the electrolyte system, which provides different properties in different regions of the electrochemical process. The acidic condition suppresses water electrolysis at the electrodes while allowing high-voltage lithium manganese oxide and lithium vanadium oxide materials to operate effectively.

Inventive Principle:

Principle #3Local quality

3Use of energy by moving object

If lithium titanium oxide is used as negative electrode material with aqueous electrolyte to achieve 2.6-2.7V electromotive force, then the energy density is improved, but the cycle life deteriorates due to hydrogen generation and active material peeling

Engineering Contradiction:

Improveenergy densityVSAvoidcycle life

Core Design Contradiction:

Use of energy by moving objectVSDuration of action of stationary object

Solution Approach 1:

The patent changes the pH parameter to 0 or less, which suppresses the hydrogen evolution reaction that occurs at lithium titanium oxide electrodes in neutral or alkaline aqueous electrolytes. This parameter change prevents hydrogen generation and the subsequent peeling of active material from the current collector, thereby extending cycle life while maintaining high energy density.

Inventive Principle:

Principle #35Parameter changes

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 improves charge-and-discharge efficiency and cycle life performance by suppressing hydrogen generation and reducing internal resistance, while maintaining safety and cost-effectiveness.

Implementation Method 1

maintaining a pH of 0 or less, which promotes ionization and forms a solid electrolyte interface

Methodology Applied

Scientific EffectIonization: Ionisation

Implementation Method 2

forms a solid electrolyte interface to enhance charge-discharge properties and cycle life

Methodology Applied

Scientific EffectSolid electrolyte interface formation:

Implementation Method 3

it is necessary that the potential range to perform charge/discharge of a battery is set to the potential range which does not causes an electrolysis reaction of water contained as a solvent

Methodology Applied

Scientific EffectElectrolysis suppression: Electrolysis

Data Source

PatentUS11024879B2Secondary battery, battery pack, and vehicle

Publication Date: 2021.06.01 KK TOSHIBA

AI summary

According to one embodiment, a secondary battery is provided. The secondary battery includes a positive electrode, a negative electrode, and an aqueous electrolyte containing alkali metal ions. The aqueous electrolyte contains an organic compound containing a carboxyl group or carboxylate group and a hydroxyl group. The pH of the aqueous electrolyte is 0 or less. The ratio of the weight of the organic compound to the weight of the aqueous electrolyte is within a range of 0.01% by weight to 6.5% by weight. The number of carbon atoms in the organic compound is 5 or more.