Lithium-Excess Battery with Amorphous Carbon Negative Electrode
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries using 'lithium-excess-type' positive active materials face issues with Li deposition on the negative electrode during high-potential formation, leading to deteriorated cycle performance and low power performance in low SOC regions, while using amorphous carbon reduces battery capacity due to high irreversible capacity during initial charge-discharge.
Innovation Solution
A nonaqueous electrolyte secondary battery design incorporating a positive electrode with a lithium transition metal composite oxide of α-NaFeO2-type crystal structure and a negative electrode with a mixture of graphite and amorphous carbon, where the amorphous carbon ratio is between 5 to 60% by mass, to suppress Li deposition and enhance battery capacity and power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lithium-excess-type positive active material is used, then discharge capacity is improved, but Li deposition occurs on negative electrode during high-potential formation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the lithium content (1.05 ≤ x < 1.20) and composition ratios of transition metals in the positive active material, while also controlling the amorphous carbon content (5-60% by mass) in the negative electrode. These parameter optimizations enable the battery to achieve high discharge capacity without Li deposition, resolving the contradiction between capacity improvement and cycle performance maintenance.
2Reliability
If amorphous carbon is used as negative active material, then Li deposition is suppressed, but battery capacity is reduced due to high irreversible capacity
Solution Approach 1:
The patent optimizes the amorphous carbon content parameter to a specific range (5-60% by mass) rather than using pure amorphous carbon. This parameter control balances the suppression of Li deposition with the reduction of irreversible capacity, maintaining high battery capacity while preventing deposition issues.
Solution Approach 2:
The patent uses a composite negative electrode material consisting of amorphous carbon combined with other carbon materials. This composite structure leverages the advantages of amorphous carbon (deposition suppression) while compensating for its disadvantages (high irreversible capacity), thereby maintaining high battery capacity.
3Quantity of substance
If high-potential formation is performed, then charge capacity is improved, but Li deposition occurs on negative electrode
Solution Approach 1:
The patent controls the composition parameters of the positive active material (lithium content x between 1.05-1.20 and transition metal ratios) to enable high-potential formation without excessive lithium extraction. This parameter optimization allows achieving high charge capacity while preventing the conditions that lead to Li deposition on the negative electrode.
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 battery achieves high capacity and power while preventing Li deposition on the negative electrode during high-potential formation, with optimal amorphous carbon ratios improving low SOC region performance and maintaining initial efficiency.
Implementation Method 1
a positive active material containing a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure... capable of inserting/extracting lithium ions
Implementation Method 2
a nonaqueous electrolyte having lithium ion conductivity
Implementation Method 3
a negative electrode containing a negative active material containing a carbon material that is a mixture of graphite and amorphous carbon... capable of inserting/extracting lithium ions
Data Source
AI summary
Provided is a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the positive electrode has a positive active material containing a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure and represented by the composition formula: Li1+αMe1−αO2 (wherein Me is a transition metal element including Co, Ni and Mn; and α>0), and the negative electrode has a negative active material which contains a carbon material that is a mixture of graphite and amorphous carbon and in which the ratio of the amorphous carbon contained in the carbon material is 5 to 60% by mass.