Phosphorus-Oxygen Electrolyte Additives for Low-Cobalt Cathode Cycling
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Solution Overview
Problem
Secondary batteries with low-cobalt or cobalt-free positive electrode active materials face challenges in lithium ion diffusion rates and cycling performance due to the limited availability and high cost of cobalt, which affects their energy storage capabilities and longevity.
Innovation Solution
Incorporating a compound with a phosphorus-oxygen double bond, such as lithium difluorophosphate, into the electrolyte solution to form a protective film on the positive electrode active material, stabilizing lithium ions and preventing over-dilithiation, while also using fluoroethylene carbonate and lithium fluorosulfonylimide to enhance cycling and rate performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cobalt content in positive electrode active material is reduced or eliminated, then cost is reduced and resource availability is improved, but lithium ion diffusion rate decreases and cycling performance deteriorates
Solution Approach 1:
The patent introduces a compound containing phosphorus-oxygen double bond as an intermediary substance in the electrolyte solution. This compound mediates between the low-cobalt positive electrode material and lithium ions, forming a protective film that facilitates lithium ion diffusion and stabilizes the electrode surface, thereby compensating for the reduced cobalt content and maintaining cycling performance.
Solution Approach 2:
The patent changes the chemical composition parameters of the electrolyte solution by introducing a compound with phosphorus-oxygen double bond (such as lithium difluorophosphate). This parameter change in the electrolyte composition enables the formation of a protective interface film that improves lithium ion diffusion kinetics, offsetting the negative effects of reduced cobalt content in the positive electrode active material.
2Quantity of substance
If cobalt content in positive electrode active material is reduced or eliminated, then cost is reduced, but lithium ion diffusion rate decreases
Solution Approach 1:
The compound containing phosphorus-oxygen double bond acts as a mediator that enhances lithium ion diffusion. It forms a protective film with favorable ion conductivity on the positive electrode surface, facilitating faster lithium ion transport and compensating for the reduced diffusion rate caused by lower cobalt content.
Solution Approach 2:
By modifying the electrolyte composition to include a compound with phosphorus-oxygen double bond, the patent changes the interfacial properties between electrolyte and electrode. This parameter change in electrolyte composition leads to improved lithium ion diffusion kinetics at the electrode surface, offsetting the slowdown caused by reduced cobalt content.
3Reliability
If compound with phosphorus-oxygen double bond is added to electrolyte solution, then lithium ion diffusion rate and cycling performance improve, but gas evolution increases
Solution Approach 1:
The patent optimizes the concentration parameter of the phosphorus-containing compound in the electrolyte solution. By controlling the content within a specific range (0.01-5% by mass), the patent achieves the balance between forming sufficient protective film for improved cycling performance and minimizing gas evolution side reactions.
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 solution significantly improves the lithium ion diffusion rate, cycling performance, and high-temperature storage capabilities of secondary batteries, maintaining energy density and rate performance without increasing gas evolution or deteriorating the battery's stability.
Implementation Method 1
Incorporating a compound with a phosphorus-oxygen double bond, such as lithium difluorophosphate, into the electrolyte solution to form a protective film on the positive electrode active material
Implementation Method 2
the O atom in the compound comprising a phosphorus-oxygen double bond can fully bond with the lithium ions on the surface of the low-cobalt or cobalt-free positive electrode active material
Implementation Method 3
Secondary batteries rely on lithium ions to intercalate and deintercalate back and forth between the positive and negative electrodes for charging and discharging
Implementation Method 4
cobalt contributes a lot to the lithium ion diffusion rate of the positive electrode active material
Implementation Method 5
using fluoroethylene carbonate and lithium fluorosulfonylimide to enhance cycling and rate performance
Data Source
AI summary
A secondary battery includes an electrolyte solution and a positive electrode plate. The positive electrode plate includes a layered material with a molecular formula of LiaNibCocM1dM2eOfAg, where M1, M2, A, a, b, c, d, e, f, and g are defined herein. The electrolyte solution includes a compound including a phosphorus-oxygen double bond that includes one or more of lithium difluorophosphate, diethyl (2-cyanoethyl)phosphonate, tripropyl phosphoric anhydride, diethyl acetyl phosphate, and triphenyl phosphate. Based on a total mass of the electrolyte solution, a percentage mass content x % of the compound including a phosphorus-oxygen double bond satisfies 0<x≤1.0. The secondary battery satisfies c+x/10≥0.10.