Hollow Positive Electrode Particles for Thermal Stability

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Solution Overview

Problem

The adherence of carbon black to carbon materials in nonaqueous electrolyte secondary cells can lead to slippage during charging and discharging, causing degraded thermal stability and enhanced heat generation, particularly during overcharging.

Innovation Solution

The use of carbon-black-adhered carbon-based negative electrode active material particles with a graphite structure, where the average short diameter of carbon black particles and the average inner diameter of hollow portions in positive electrode active material particles maintain a specific ratio (1.2≦B/A≦260), effectively trapping freed carbon black particles and enhancing thermal stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If carbon black is caused to adhere to the surface portion of a carbon material, then low-temperature characteristic is improved, but thermal stability is degraded and heat generation is enhanced during overcharging

Engineering Contradiction:

Improvelow-temperature characteristicVSAvoidthermal stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The hollow portion in the positive electrode active material particle acts as an intermediary structure to capture and contain carbon black particles that slip off during charging and discharging. This mediator prevents the carbon black from being freed into the electrolytic solution, thereby maintaining both the low-temperature characteristic improvement and preventing thermal stability degradation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Instead of treating the slipped carbon black particles as harmful contaminants to be eliminated, the invention converts this potential harm into a benefit by providing hollow portions that specifically capture these particles. The carbon black particles that would otherwise degrade thermal stability are now contained within the hollow portions, preventing them from being freed into the electrolytic solution while maintaining their beneficial low-temperature performance enhancement.

Inventive Principle:

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

2Duration of action of moving object

If carbon black adhered to the surface portion slips off during charging and discharging, then expansion and contraction of carbon material occurs, but carbon black freed into electrolytic solution absorbs charge carriers causing enhanced heat generation

Engineering Contradiction:

Improvecharging and discharging cycleVSAvoidheat generation

Core Design Contradiction:

Duration of action of moving objectVSObject-generated harmful factors

Solution Approach 1:

The invention converts the harmful effect of slipped carbon black particles being freed into the electrolytic solution into a beneficial containment mechanism. The hollow portions in the positive electrode active material particles specifically capture these particles, preventing them from absorbing charge carriers and generating heat, while allowing the charging and discharging cycles to proceed normally.

Inventive Principle:

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

Solution Approach 2:

The hollow portions serve as an intermediary structure between the slipped carbon black particles and the electrolytic solution. Instead of allowing direct contact between the carbon black particles and the electrolytic solution (which causes heat generation), the hollow portions mediate by containing the particles, thereby preventing the harmful interaction while maintaining the charging and discharging functionality.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 configuration suppresses heat generation during overcharging by physically adsorbing carbon black particles within the hollow portions of the positive electrode active material, thereby improving thermal stability and cell performance.

Implementation Method 1

physically adsorbing carbon black particles within the hollow portions of the positive electrode active material

Methodology Applied

Scientific EffectPhysical adsorption: Physisorption

Data Source

PatentUS9825299B2Nonaqueous electrolyte secondary cell

Publication Date: 2017.11.21 TOYOTA JIDOSHA KK

AI summary

Provided is a nonaqueous electrolyte secondary cell in which heat generation is suppressed. The nonaqueous electrolyte secondary cell according to the invention has a positive electrode including positive electrode active material particles and a negative electrode including negative electrode active material particles. The negative electrode active material particles are carbon-black-adhered carbon-based negative electrode active material particles which are constituted by a carbon material having a graphite structure in at least part thereof and which have carbon black (CB) particles that have adhered to at least part of a surface portion. The positive electrode active material particles are of a hollow structure having a shell and a hollow portion. The average short diameter A of the CB particles in the carbon-black-adhered carbon-based negative electrode active material particles and an average inner diameter B of the hollow portions in the positive electrode active material particles fulfill the relationship: 1.2≦B/A≦260.