Positive Electrode Composition Balancing Density and Rate Performance
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in achieving higher energy density, cycling performance, and kinetic performance due to irreversible capacity loss and solid electrolyte interphase (SEI) formation during the first charge process.
Innovation Solution
A positive electrode plate is designed with a specific composition and structure, incorporating a first positive electrode active material represented by chemical formula Li1+xAaFeyMnzTivPO4−wSw and a second positive electrode active material represented by chemical formula Li2+rNasM1+qO2+t, which work synergistically to enhance energy density and cycling stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If lithium metal powder or stabilized lithium metal powder is added to negative electrode slurry for lithium supplementation, then energy density can be improved, but production safety deteriorates due to high reactivity with moisture in air
Solution Approach 1:
The patent introduces a lithium supplement agent as an intermediary substance that provides lithium ions to the negative electrode without the safety hazards of lithium metal powder. This agent acts as a mediator between the need for lithium supplementation and the requirement for production safety, enabling lithium ion release in a controlled manner without direct exposure to reactive lithium metal.
Solution Approach 2:
The patent changes the chemical form and properties of the lithium supplementation material from reactive lithium metal powder to a safer lithium supplement agent with controlled lithium ion release characteristics. This parameter change transforms the supplementation approach from one requiring stringent safety measures to one that can be handled under normal production conditions.
2Reliability
If a large amount of solid electrolyte interphase (SEI) is generated on the negative electrode surface during first charge, then the battery structure is formed, but irreversible capacity loss increases and energy density decreases
Solution Approach 1:
The patent applies lithium supplement agent to the negative electrode before battery assembly and initial charging. This preliminary action ensures that lithium ions are already present and available when the SEI forms during first charge, preventing excessive consumption of active lithium and reducing irreversible capacity loss from the outset.
Solution Approach 2:
The lithium supplement agent on the negative electrode automatically releases lithium ions during the SEI formation process, providing self-service compensation for the lithium consumed in forming the protective interface. This eliminates the need for external lithium supplementation and reduces net lithium loss.
3Use of energy by moving object
If high compacted density is achieved in the positive electrode plate, then energy density improves, but rate performance deteriorates due to reduced ion and electron transport
Solution Approach 1:
The patent applies different materials and structures to different regions of the positive electrode plate. The surface region contains catalyst particles and conductive materials to enhance reaction kinetics and electron transport, while the bulk region maintains high density for energy storage. This local differentiation allows simultaneous optimization of rate performance and energy density.
Solution Approach 2:
The patent creates a composite positive electrode structure combining active material particles with conductive additives and catalyst particles. This composite material approach enables the electrode to maintain high compacted density while providing sufficient pathways for ion and electron transport, resolving the contradiction between density and rate performance.
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 proposed positive electrode plate effectively increases the specific discharge capacity of lithium-ion secondary batteries, thereby enhancing energy density, while also improving cycling stability and rate performance.
Implementation Method 1
In the first charge process of the lithium-ion secondary batteries, a large amount of solid electrolyte interphases (Solid Electrolyte Interphase, SEI) are generated on the surface of a negative electrode, consuming limited lithium ions and electrolytes
Implementation Method 2
a large amount of solid electrolyte interphases (Solid Electrolyte Interphase, SEI) are generated on the surface of a negative electrode, consuming limited lithium ions and electrolytes
Data Source
AI summary
A positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, where the positive electrode active material layer includes a first positive electrode active material represented by chemical formula (1) and a second positive electrode active material represented by chemical formula (2): Li1+xAaFeyMnzTivPO4−wSw (1), and Li2+rNasM1+qO2+t (2); and the positive electrode plate satisfies: 5.2≤R/Q≤13.5. Such a positive electrode plate can achieve a high specific discharge capacity of the electrochemical apparatus, thereby increasing energy density of the electrochemical apparatus. In addition, a relationship between compacted density R and single surface density Q of the positive electrode plate is limited, effectively improving cycling stability and rate performance of the electrochemical apparatus.