Negative Electrode Granules for Lower Short-Circuit Heat

Solution Overview

Problem

Conventional lithium-ion secondary batteries face challenges in inhibiting heat generation during short circuits while maintaining battery capacity, as graphite-based particles facilitate high short-circuit currents and lithium titanate oxide particles reduce capacity.

Innovation Solution

A method of producing a negative electrode for lithium-ion secondary batteries involves mixing lithium titanate oxide particles, a binder, and a solvent to create a particle-dispersed liquid, which is then used to granulate graphite-based particles, forming wet granules that are subsequently processed into a negative electrode composite material layer with controlled distribution of lithium titanate oxide particles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If graphite-based particles are used as negative electrode active material, then battery capacity is improved, but heat generation during short circuit increases

Engineering Contradiction:

Improvebattery capacityVSAvoidheat generation during short circuit

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The patent applies local quality by creating wet granules where LTO particles are locally concentrated at the boundaries between graphite-based particles, rather than uniformly distributed. This localized placement specifically targets the short-circuit current paths (which flow at particle boundaries) with high-resistance LTO material, while preserving the high-capacity graphite particles in the interior. The granulation process naturally creates this non-uniform distribution with LTO enrichment at granule surfaces and boundaries.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses LTO particles as an intermediary material that mediates between graphite-based particles. The LTO particles form a barrier layer at the boundaries, preventing direct electrical contact between graphite particles and thereby blocking short-circuit current paths. This intermediary approach allows the system to maintain graphite's high capacity while introducing LTO's high resistance property at critical locations.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-generated harmful factors

If LTO particles are mixed with graphite-based particles to reduce short-circuit current, then heat generation is reduced, but battery capacity decreases

Engineering Contradiction:

Improveheat generation during short circuitVSAvoidbattery capacity

Core Design Contradiction:

Object-generated harmful factorsVSQuantity of substance

Solution Approach 1:

The patent segments the negative electrode into distinct functional zones within each granule: graphite-based particles form the capacity-providing core, while LTO particles form the boundary/protection layer. This segmentation allows each material to perform its optimal function - graphite for capacity and LTO for short-circuit suppression - without the capacity penalty of uniform mixing.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by creating wet granules where LTO particles are locally concentrated at the boundaries between graphite-based particles, rather than uniformly distributed. This localized placement specifically targets the short-circuit current paths (which flow at particle boundaries) with high-resistance LTO material, while preserving the high-capacity graphite particles in the interior. The granulation process naturally creates this non-uniform distribution with LTO enrichment at granule surfaces and boundaries.

Inventive Principle:

Principle #3Local quality

3Object-generated harmful factors

If a large quantity of LTO particles is included to reduce graphite contact area, then short-circuit current is reduced, but battery capacity decreases

Engineering Contradiction:

Improveshort-circuit currentVSAvoidbattery capacity

Core Design Contradiction:

Object-generated harmful factorsVSQuantity of substance

Solution Approach 1:

The patent applies partial action by using a relatively small amount of LTO particles (2-15 mass%) concentrated at critical locations (granule boundaries), rather than requiring large quantities for uniform distribution. This partial placement at key positions achieves effective short-circuit suppression without the capacity penalty of high overall LTO content.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS12308436B2Method of producing negative electrode, negative electrode, and lithium-ion secondary battery

Publication Date: 2025.05.20 TOYOTA JIDOSHA KK

AI summary

A method of producing a negative electrode includes at least the following (A) to (C): (A) mixing powder consisting of lithium titanate oxide particles, a binder, and a solvent to prepare a particle-dispersed liquid; (B) granulating powder consisting of graphite-based particles by using the particle-dispersed liquid to prepare wet granules; and (C) forming the wet granules into a negative electrode composite material layer to produce a negative electrode. The negative electrode composite material layer is formed so as to include the lithium titanate oxide particles in an amount not lower than 2 mass % and not higher than 15 mass % of the total amount of the graphite-based particles and the lithium titanate oxide particles.