Nonaqueous Electrolyte Battery Voltage Stability

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Solution Overview

Problem

Nonaqueous electrolyte secondary batteries suffer from oxidation decomposition near the positive electrode, leading to parasitic resistance and reduced high temperature cycle capability due to the accumulation of decomposition products on the negative electrode.

Innovation Solution

A nonaqueous electrolyte secondary battery design featuring a positive electrode with a potential of 4.4 V or higher and a negative electrode with a potential of 1.0 V or higher, utilizing a nonaqueous solvent composition of 80-95% diethyl carbonate, and an imide lithium salt to suppress oxidation decomposition and improve conductivity, along with a separator impregnated with the electrolyte.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If LiMn1.5Ni0.5O4 positive electrode with potential of 4.9-5.0 V is used to increase battery voltage, then battery voltage increases to close to 5 V, but oxidation decomposition of nonaqueous electrolyte occurs near positive electrode

Engineering Contradiction:

Improvebattery voltageVSAvoidhigh temperature cycle capability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent changes the chemical composition parameters of the nonaqueous electrolyte by specifying precise volume ratios of diethyl carbonate (80-95%), ethylene carbonate (5-15%), and propylene carbonate (5-15%), along with specific concentrations of lithium salts. This parameter optimization suppresses oxidation decomposition at high potentials while maintaining adequate ionic conductivity, resolving the contradiction between high battery voltage and reliability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite electrolyte system combining multiple carbonate solvents (diethyl carbonate, ethylene carbonate, propylene carbonate) with lithium salts. This composite formulation leverages the complementary properties of each component: diethyl carbonate provides high voltage stability, while ethylene carbonate and propylene carbonate enhance ionic conductivity and suppress decomposition, collectively improving high temperature cycle capability at 4.9-5.0 V operation.

Inventive Principle:

Principle #40Composite materials

2Power

If nonaqueous electrolyte is used in high potential state, then battery voltage increases, but oxidation decomposition occurs and decomposition products accumulate on negative electrode

Engineering Contradiction:

Improvebattery voltageVSAvoidparasitic resistance

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent optimizes the electrolyte composition parameters to suppress oxidation decomposition reactions. By adjusting the volume ratios of carbonate solvents and lithium salt concentrations, the patent minimizes the formation of decomposition products that would otherwise accumulate on the negative electrode and increase parasitic resistance, enabling stable high voltage operation.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potential harm of electrolyte decomposition into a beneficial outcome by formulating an electrolyte composition that preferentially forms stable surface films on electrodes. These films, while products of decomposition, actually protect the electrodes from further degradation and reduce parasitic resistance over time, improving overall battery performance and cycle stability.

Inventive Principle:

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

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 battery exhibits enhanced high temperature cycle capability, with improved capacity maintenance ratios and reduced parasitic resistance, as demonstrated by charging and discharging cycle tests at elevated temperatures.

Implementation Method 1

A nonaqueous electrolyte secondary battery that exerts charging and discharging through migration of Li ions between a negative electrode and a positive electrode

Methodology Applied

Scientific EffectIonic conduction: Conduction (electrical)

Implementation Method 2

a separator disposed between the negative electrode and the positive electrode

Methodology Applied

Scientific EffectPhysical separation: Physical Containment

Implementation Method 3

The nonaqueous electrolyte comprises a nonaqueous solvent including diethyl carbonate and at least one of ethylene carbonate and propylene carbonate

Methodology Applied

Scientific EffectElectrolyte conduction: Electrolyte

Data Source

PatentUS7601463B2Nonaqueous electrolyte secondary battery

Publication Date: 2009.10.13 KK TOSHIBA

AI summary

A nonaqueous electrolyte secondary battery includes: an outer housing; a nonaqueous electrolyte filled in the outer housing, a positive electrode housed in the outer housing, a negative electrode housed in the outer housing and a separator disposed between the negative electrode and the positive electrode. The nonaqueous electrolyte comprises a nonaqueous solvent including diethyl carbonate and at least one of ethylene carbonate and propylene carbonate, and the nonaqueous electrolyte has a content of the diethyl carbonate of from 80 to 95% by volume. The positive electrode comprises a positive electrode active substance having a positive electrode potential in a full charged state of 4.4 V or higher with respect to a potential of metallic lithium. The negative electrode comprises a negative electrode active substance having a negative electrode potential in a full charged state of 1.0 V or higher with respect to a potential of metallic lithium.