Bow-Shaped Carbon Negative Electrode for Li-Ion Batteries
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Solution Overview
Problem
Lithium ion secondary batteries experience capacity degradation due to repeated charge and discharge cycles, storage in a charged state, and float charging, primarily attributed to the lower charge/discharge efficiency of the negative electrode, leading to irreversible changes in the operation ranges of electrode potentials and reduced battery capacity.
Innovation Solution
A carbon material for the negative electrode is developed using raw petroleum coke, processed through delayed coking, pulverization, carbonization, and graphitization, with specific conditions to achieve a structure of stacked plates curved into a bow shape, enhancing lithium diffusion and reducing capacity degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional carbon materials are used as negative electrode, then high energy density per unit volume is achieved, but capacity degradation occurs due to lower charge/discharge efficiency
Solution Approach 1:
The invention changes the structural parameters of graphite particles by controlling the coking process conditions (temperature 400-600°C, pressure 400-800 kPa) and raw material composition to achieve a specific bow-shaped curved plate structure with controlled plate thickness and curvature radius, which improves charge/discharge efficiency while maintaining high energy density
Solution Approach 2:
The invention uses composite raw materials consisting of multiple components (petroleum coke, coal tar pitch, mesophase pitch) in specific ratios to create a composite carbon material with optimized properties that combines high energy density with improved charge/discharge efficiency and reduced capacity degradation
2Use of energy by moving object
If graphite-based carbon materials are used, then high energy density per unit volume is achieved, but irreversible changes in electrode potential operation ranges occur
Solution Approach 1:
The invention optimizes process parameters including coking temperature (400-600°C), pressure (400-800 kPa), and holding time to control the formation of the bow-shaped curved plate structure, which stabilizes the electrode potential operation range while maintaining high energy density
Solution Approach 2:
The invention skips the conventional high-temperature graphitization process (2000-3000°C) by achieving the desired curved plate structure at lower coking temperatures, thereby preventing irreversible structural changes and stabilizing the electrode potential operation range
3Shape
If delayed coking is performed at high temperature and pressure, then curved plate structure is formed, but production complexity increases
Solution Approach 1:
The invention optimizes the coking process parameters (temperature 400-600°C, pressure 400-800 kPa, holding time) to achieve the bow-shaped curved plate structure under milder conditions than conventional methods, simplifying the production process while maintaining the desired shape
Solution Approach 2:
The invention uses specific raw materials (petroleum coke, coal tar pitch, mesophase pitch) as intermediaries that facilitate the formation of the curved plate structure during coking, enabling the desired shape to be achieved more easily and with less process complexity
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 carbon material maintains high charge/discharge capacity and suppresses capacity degradation, ensuring high reliability for lithium ion secondary batteries, particularly suitable for applications in automobiles and power storage infrastructure.
Implementation Method 1
when a heavy oil is treated at high temperatures, thermal decomposition and polycondensation reactions will occur
Implementation Method 2
thermal decomposition and polycondensation reactions will occur, liquid crystal spherules referred to as 'mesophase' are formed
Implementation Method 3
calcining the raw coke material powder at 1000 to 1500°C for carbonization to obtain calcined coke
Implementation Method 4
pulverizing and graphitizing the calcined coke at a temperature of 2200 to 2800°C to obtain graphitized coke
Data Source
Figure 1~2(b)
Figure 3~4
AI summary
There is provided a carbon material for a negative electrode of a lithium ion secondary battery which is capable of maintaining a high level of charge and discharge capacity and suppressing capacity degradation which will occur due to repetition of a charge and discharge cycle, storage under a charged state, and float charging. The carbon material for a negative electrode of a lithium ion secondary battery includes: particles having a structure including a plurality of stacked plates which are prepared from a raw coke materials obtained by a delayed coking method, where the ratio of the total of the generation rate (mass%) of a hydrogen gas, a hydrocarbon gas having one carbon atom (C1 gas), and a hydrocarbon gas having two carbon atoms (C2 gas) to be generated by subjecting a heavy oil to coking and the formation rate (mass%) of a raw coke materials satisfies the condition: total of generation rate/formation rate = 0.30 to 0.60, and where the structure is curved into a bow shape, and where, in each of the plates, an average plate thickness is defined as T, an average bow height including the plate thickness is defined as H, and an average length in the vertical direction is defined as L, L/T is 5.0 or more and H/T is from 1.10 to 1.25.