Graphite Negative Electrode Coating for Lithium Ion Battery Efficiency
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Solution Overview
Problem
Lithium ion secondary batteries using carbon-coated graphite as negative electrodes face a trade-off between initial charge and discharge efficiency and rate characteristics, with existing techniques failing to improve both simultaneously due to excessive low-crystallinity carbon coating leading to increased irreversible capacity and side reactions.
Innovation Solution
A negative electrode active material is developed with graphite powder coated by a carbon material of lower crystallinity, where the specific surface area is between 0.8 and 5.3 m^2/g, and DBP absorption is between 34 and 43 cm^3/100g, optimizing the coating amount and surface area to enhance binding properties and lithium ion diffusion, thereby improving charge-discharge characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the edge surface of natural graphite is coated with carbon having lower crystallinity to suppress side reactions with electrolytic solution, then stability is improved, but charge and discharge efficiency decreases due to increased irreversible capacity
Solution Approach 1:
The patent optimizes the coating amount of low-crystallinity carbon to a specific range (0.1-5.0 mass%) to balance stability and charge-discharge efficiency. By precisely controlling this parameter, the invention achieves both suppressed side reactions and maintained lithium ion diffusion, resolving the contradiction between reliability and productivity
Solution Approach 2:
The invention uses a composite structure combining natural graphite core with low-crystallinity carbon coating. This composite material leverages the high capacity of natural graphite while using the coating layer to suppress side reactions, achieving both stability and efficiency simultaneously
2Reliability
If a large amount of low crystalline carbon is used to coat graphite, then side reactions with electrolytic solution are suppressed, but irreversible capacity increases and charge-discharge efficiency deteriorates
Solution Approach 1:
The patent applies partial action by using a controlled, limited amount of low-crystallinity carbon coating (0.1-5.0 mass%) rather than excessive coating. This partial coverage is sufficient to suppress side reactions while minimizing the formation of dead carbon that would cause irreversible capacity loss, thus resolving the contradiction between reliability and energy loss
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 optimized negative electrode active material achieves superior charge-discharge characteristics by balancing initial efficiency and rate performance, reducing irreversible capacity and improving lithium ion intercalation and deintercalation, leading to enhanced battery stability and performance.
Implementation Method 1
graphite powder, in which at least a part of a surface of the graphite powder is coated with a carbon material having lower crystallinity than the graphite powder
Implementation Method 2
specific surface area measured using a nitrogen adsorption BET method is more than or equal to 0.8 m^2/g and less than or equal to 5.3 m^2/g
Implementation Method 3
DBP absorption measured according to JIS K 6217-4 is more than or equal to 34 cm^3/100g and less than or equal to 43 cm^3/100g
Data Source
Figure 1~2
AI summary
A negative electrode for a lithium ion secondary battery according to the present invention includes a negative electrode active material and a binder, in which the negative electrode active material satisfies the following requirements (A), (B), and (C): (A) graphite powder is used as a core material, and at least a part of a surface of the graphite powder is coated with a carbon material having lower crystallinity than the graphite powder; (B) a specific surface area measured using a nitrogen adsorption BET method is more than or equal to 0.8 m2/g and less than or equal to 5.3 m2/g; and (C) an amount of dibutyl phthalate absorption measured according to JIS K 6217-4 is more than or equal to 32 cm3/100 g and less than or equal to 45 cm3/100 g.