Non-aqueous Electrolyte Secondary Cell Voltage Control

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Solution Overview

Problem

Non-aqueous electrolyte secondary cells with lithium-transition metal complex oxides as positive electrodes and carbon materials as negative electrodes exhibit poor charge-discharge cycle performance due to capacity degradation, despite efforts to control lithium content and suppress electrolyte decomposition.

Innovation Solution

Controlling the end-of-discharge voltage of these cells to 2.9 V or higher using a control circuit to prevent the reduction of the positive electrode potential, thereby reducing manganese dissolution and maintaining the crystal structure of the positive electrode, which enhances charge-discharge cycle performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the end-of-discharge voltage is set lower (2.0-2.5 V) to maximize capacity utilization, then the cell capacity is improved, but the positive electrode crystal structure degrades and manganese dissolves into the electrolyte

Engineering Contradiction:

Improvecell capacityVSAvoidpositive electrode crystal structure

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The patent changes the voltage parameter by setting the end-of-discharge voltage to 2.9 V or higher, which prevents the reduction of the positive electrode potential below 4.0 V. This parameter change stops manganese dissolution and maintains the crystal structure stability while still achieving practical capacity utilization.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If the positive electrode potential is reduced below 4.0 V to extract more capacity, then the cell capacity is improved, but manganese dissolves into the electrolyte causing capacity degradation

Engineering Contradiction:

Improvecell capacityVSAvoidcharge-discharge cycle performance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies preliminary anti-action by establishing a voltage control mechanism that prevents the positive electrode potential from dropping below 4.0 V. This preemptive measure stops manganese dissolution before it can occur, thereby maintaining reliability and charge-discharge cycle performance.

Inventive Principle:

Principle #9Preliminary anti-action

3Reliability

If the end-of-discharge voltage is set higher (2.9 V or higher) to maintain crystal structure stability, then the charge-discharge cycle performance is improved, but the available capacity is reduced

Engineering Contradiction:

Improvecharge-discharge cycle performanceVSAvoidcell capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent optimizes the voltage parameter by setting the end-of-discharge voltage to 2.9 V or higher, finding the optimal balance point that maintains crystal structure stability and prevents manganese dissolution while still achieving practical capacity utilization for the battery system.

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

This approach effectively suppresses capacity degradation and improves charge-discharge cycle performance by maintaining the stability of the positive electrode's crystal structure and preventing manganese dissolution into the electrolyte.

Implementation Method 1

controlling discharge of the secondary cell... so that an end-of-discharge voltage of the secondary cell is 2.9 V or higher thereby preventing reduction of a positive electrode potential

Methodology Applied

Scientific EffectElectrochemical potential:

Implementation Method 2

reducing manganese dissolution and maintaining the crystal structure of the positive electrode

Methodology Applied

Scientific EffectDissolution:

Implementation Method 3

a positive electrode active material containing a lithium-transition metal complex oxide having a layered structure... capable of intercalating and deintercalating lithium ions

Methodology Applied

Scientific EffectIntercalation:

Data Source

PatentUS8253386B2Method of controlling charge and discharge of non-aqueous electrolyte secondary cell

Publication Date: 2012.08.28 PANASONIC ENERGY CO LTD

AI summary

Capacity degradation due to charge/discharge cycles is suppressed in either a non-aqueous electrolyte secondary cell provided with a positive electrode including, as a positive electrode active material, a lithium-transition metal complex oxide having a layered structure and containing at least Ni and Mn as transition metals, and a negative electrode containing a carbon material as a negative electrode active material and having a higher initial charge-discharge efficiency than that of the positive electrode, or an assembled battery having a plurality of cells each of which is the secondary cell. A control circuit incorporated in the secondary cell or the assembled battery, or in an apparatus using the secondary cell or the assembled battery, monitors the voltage of the secondary cell or each of the cells in the assembled battery so that the end-of-discharge voltage of each cell is 2.9 V or higher.