Core-Shell Hard Carbon Anode Material for Higher Volumetric Capacity
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Solution Overview
Problem
Lithium ion batteries face challenges in achieving high energy density, safety performance, and cycle performance due to limitations in the existing negative electrode active materials, particularly graphite, which has a low reversible specific capacity and energy density, and is prone to self-discharge and capacity attenuation.
Innovation Solution
A negative electrode active material with a core-shell structure is developed, where hard carbon is coated with a first shell material having a volumetric specific capacity of 800 mAh/cm3 or more, and optionally includes elements like Sn, Si, or Ge, along with conductive carbon materials to enhance compaction density and volume energy density, while minimizing volume expansion and the risk of pulverization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hard carbon is used as negative electrode active material, then good cycle performance is achieved, but volume energy density is low due to low reversible specific capacity
Solution Approach 1:
The patent uses a core-shell structure where hard carbon core provides cycle stability while the alloy material shell (Sn, Si, Sb, or Ge) provides high volumetric specific capacity. This composite structure combines the advantages of both materials to achieve high volume energy density while maintaining good cycle performance.
Solution Approach 2:
The patent embeds the hard carbon core inside the alloy material shell, creating a nested core-shell structure. This allows the inner hard carbon to provide structural stability while the outer shell maximizes volumetric capacity, resolving the contradiction between cycle life and energy density.
2Quantity of substance
If alloy materials (Sn, Si, Sb, Ge) are used to increase volumetric specific capacity, then volume energy density improves, but volume expansion occurs leading to pulverization
Solution Approach 1:
The patent uses a shell structure made of alloy materials that can accommodate volume expansion during lithium insertion. The shell acts as a flexible container that prevents pulverization while allowing the necessary volume change, thus maintaining structural integrity during cycling.
Solution Approach 2:
The patent designs the shell structure with sufficient thickness and appropriate material composition to cushion the internal stress generated during volume expansion. This pre-designed structural buffer prevents crack formation and particle disintegration before they can occur during battery cycling.
3Ease of manufacture
If conventional negative electrode materials are used, then manufacturing is simple, but self-discharge and capacity attenuation are high
Solution Approach 1:
The patent changes the key parameter of volumetric specific capacity by selecting alloy materials (Sn, Si, Sb, Ge) with inherently higher capacity than conventional graphite. This parameter change reduces self-discharge and improves capacity retention while maintaining compatibility with existing manufacturing processes.
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 core-shell structure improves compaction density, reduces self-discharge, and enhances cycle and storage performance by buffering stress and preventing particle detachment from the current collector, leading to improved volume energy density and capacity retention.
Implementation Method 1
the first shell includes a first element capable of forming an alloy with Li
Data Source
AI summary
A negative electrode active material has a core-shell structure. The negative electrode active material includes a first shell and at least two core material particles located in the first shell. The core material includes hard carbon. The first shell includes a first shell material with a volumetric specific capacity of 800 mAh/cm3 or more.