Amorphous Carbon-Coated Graphite Negative Electrode for High-Temperature Life

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Solution Overview

Problem

Conventional amorphous carbon-coated graphite negative electrodes in non-aqueous secondary batteries suffer from cracking and reduced capacity at high temperatures due to exposure of natural graphite during pressing, leading to poor high-temperature life characteristics and capacity retention.

Innovation Solution

A negative electrode comprising a mixture of amorphous carbon-coated graphite (density ≤1.50 g/cm3) and a hard carbon-based material (density ≥1.65 g/cm3) at a specific weight ratio (90:10 to 99:1) is used, which suppresses cracking and reaction with the electrolyte, enhancing packing density and stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If amorphous carbon-coated graphite is densely packed to increase capacity, then the battery capacity increases, but cracks are generated during pressing and the natural graphite interior is exposed to electrolyte, causing capacity degradation

Engineering Contradiction:

Improvebattery capacityVSAvoidhigh-temperature life characteristics

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent uses a composite coating structure consisting of amorphous carbon and crystalline carbon (graphite) layers on natural graphite particles. This composite material approach allows the amorphous carbon to provide crack resistance while the crystalline carbon maintains structural stability, preventing electrolyte penetration even under dense packing conditions. The combination of different carbon forms creates a synergistic effect that simultaneously improves capacity and reliability.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The negative electrode is subjected to pressing treatment before battery assembly, which pre-compresses the electrode structure and reduces subsequent expansion during initial charging cycles. This preliminary action prevents crack formation during battery operation by eliminating the mechanical stress that would otherwise expose natural graphite to electrolyte, thereby maintaining capacity stability over extended cycles at high temperatures.

Inventive Principle:

Principle #10Preliminary action

2Volume of stationary object

If the negative electrode is pressed at high pressure to improve packing density, then capacity increases, but the amorphous carbon coating cracks and exposes natural graphite to electrolyte

Engineering Contradiction:

Improvepacking densityVSAvoidelectrolyte reaction

Core Design Contradiction:

Volume of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The dual-layer carbon coating (amorphous + crystalline) creates a composite protective barrier that is more resistant to cracking under compression than single-layer coatings. The amorphous carbon provides flexibility and crack resistance, while the crystalline graphite maintains structural integrity, together preventing electrolyte contact with natural graphite even when pressed to high densities.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent optimizes the thickness ratio and composition of the amorphous and crystalline carbon layers to achieve the right balance between flexibility and structural strength. By controlling these parameters, the coating can withstand pressing-induced stresses without cracking, maintaining its protective function against electrolyte penetration while allowing high packing density.

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If conventional amorphous carbon coating is used to protect natural graphite, then initial capacity is maintained, but cracks develop during pressing and capacity retention deteriorates after 500 cycles

Engineering Contradiction:

Improveinitial capacityVSAvoidcapacity retention after 500 cycles

Core Design Contradiction:

Quantity of substanceVSDuration of action of stationary object

Solution Approach 1:

The combination of amorphous and crystalline carbon in a specific ratio creates a composite coating that maintains the protective function over extended periods. The amorphous carbon absorbs mechanical stress preventing crack initiation, while the crystalline graphite provides long-term structural stability, ensuring the coating remains intact and protective throughout 500+ charge-discharge cycles at elevated temperatures.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The amorphous carbon layer acts as a cushioning layer that absorbs and distributes mechanical stresses during pressing and cycling. This beforehand cushioning prevents stress concentration that would lead to crack formation, thereby protecting the underlying natural graphite from electrolyte contact throughout the battery's operational life, including after 500 cycles.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS10886527B2Negative electrode for non-aqueous secondary battery and non-aqueous secondary battery using the negative electrode

Publication Date: 2021.01.05 ENVISION AESC ENERGY DEVICES LTD

AI summary

Provided with a negative electrode for a secondary battery comprising an anode active material that is a mixture of an amorphous carbon-coated graphite active material A having a density of 1.50 g/cm3 or less in press pelletizing at 2 kN/cm2 and a carbon-based active material B having a density of 1.65 g/cm3 or higher in press pelletizing at 2 kN/cm2 in a weight ratio of 90:10 to 99:1 as A:B, so that the cracking of amorphous carbon-coated graphite is suppressed and high-temperature life characteristics is improved.