Reduced Graphene Coating for Higher Initial Li-Ion Battery Efficiency
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Solution Overview
Problem
Lithium ion secondary batteries using reduced graphene as the negative electrode active material suffer from low initial charge/discharge efficiency and high irreversible capacity, limiting the usable battery capacity.
Innovation Solution
A reduced graphene-based material with a coating containing lithium, phosphorus, fluorine, and oxygen, derived from lithium difluorophosphate, is used for the negative electrode, improving the charge/discharge efficiency by suppressing side reactions and reducing irreversible capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If reduced graphene is used as negative electrode active material to improve energy density, then battery energy density is improved, but initial charge/discharge efficiency decreases and irreversible capacity increases
Solution Approach 1:
A coating layer containing lithium element, phosphorus element, fluorine element, and oxygen element is introduced as an intermediary between the reduced graphene and the electrolyte. This coating layer mediates the interaction, suppressing direct harmful reactions while allowing beneficial lithium ion insertion/extraction, thereby improving initial charge/discharge efficiency without sacrificing energy density
Solution Approach 2:
The chemical composition and structure of the graphene surface are changed by applying a coating with specific elemental ratios (Li: 0.8-2.0 atomic%, P: 0.5-2.0 atomic%, F: 0.05-1.0 atomic%, O: 7.0-12.0 atomic%). This parameter change transforms the surface properties to reduce irreversible capacity while maintaining the high energy density characteristics of reduced graphene
2Use of energy by moving object
If reduced graphene is used as negative electrode active material to improve energy density, then battery energy density is improved, but irreversible capacity increases which decreases usable battery capacity
Solution Approach 1:
The coating layer acts as a protective intermediary that prevents direct contact between reduced graphene and electrolyte, thereby suppressing side reactions that cause irreversible capacity loss. This intermediary layer allows reversible lithium ion storage while blocking harmful irreversible reactions
Solution Approach 2:
The coating process, which initially modifies the graphene structure, is transformed into a beneficial process by carefully controlling the elemental composition to create a protective layer. This converts the potential harm of structural modification into the benefit of enhanced electrochemical stability and reduced irreversible capacity
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 use of the coated reduced graphene-based material enhances the initial charge/discharge efficiency and capacity of lithium ion secondary batteries, leading to improved battery performance.
Implementation Method 1
a step of heat-treating an oxidized graphene together with lithium difluorophosphate
Implementation Method 2
a coating containing lithium element (Li), phosphorus element (P), fluorine element (F), and oxygen element (O) on at least a part of the surface
Implementation Method 3
in the elemental composition of the surface as measured by X-ray photoelectron spectroscopy (XPS)
Data Source
AI summary
An object of the present invention is to provide a reduced graphene-based material to improve charge/discharge efficiency of a lithium ion secondary battery. The reduced graphene-based material of the present invention has a coating containing lithium element (Li), phosphorus element (P), fluorine element (F), and oxygen element (O) on at least a part of the surface, wherein in the elemental composition of the surface as measured by X-ray photoelectron spectroscopy (XPS), the proportion of lithium element (Li) is 0.8 to 2.0 (atomic %), the proportion of phosphorus element (P) is 0.5 to 2.0 (atomic %), the proportion of fluorine element (F) is 0.05 to 1.0 (atomic %), and the proportion of oxygen element (O) is 7.0 to 12.0 (atomic %).