Lithium Ion Capacitor Electrolyte Additive and Doping Strategy
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Solution Overview
Problem
Lithium ion capacitors face challenges in achieving high capacity retention during continuous charging at high temperatures and maintaining durability, with existing hybrid capacitors struggling to uniformly dope large-size cells and achieving high energy and output densities.
Innovation Solution
Incorporating vinylene carbonate or its derivatives in the aprotic organic solvent electrolyte solution, with the positive and/or negative electrodes being doped with lithium ions to maintain a potential of at most 2.0 V, and using a mixture of cyclic and chain carbonates as solvents, to enhance the capacitor's energy and output densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the negative electrode is doped with lithium ions to increase energy density, then the energy density is improved, but the doping requires a very long time and it tends to be difficult to uniformly dope the entire negative electrode
Solution Approach 1:
The negative electrode is divided into multiple regions with different lithium ion doping levels. The doping is performed in stages, with the center region receiving higher doping concentration than the peripheral regions, achieving uniform overall doping without requiring excessively long doping time.
Solution Approach 2:
Different regions of the negative electrode are doped with different lithium ion concentrations according to their specific requirements. The center region, which has longer ion transport paths, receives higher doping concentration to compensate for the longer diffusion distance, while peripheral regions receive lower concentration.
2Quantity of substance
If the negative electrode is doped with lithium ions to increase energy density, then the energy density is improved, but it tends to be difficult to uniformly dope large-size large capacity cells
Solution Approach 1:
The large-size negative electrode is segmented into multiple doping zones, with the doping process controlled to achieve different lithium ion concentrations in different regions. This segmentation approach enables uniform overall doping distribution across large electrodes by compensating for radial diffusion differences.
Solution Approach 2:
The doping process transitions from a simple time-based approach to a spatially-controlled process, where lithium ion concentration is optimized as a function of radial position from the electrode center. This dimensional approach to doping control enables uniform distribution across large electrodes.
3Quantity of substance
If a hybrid capacitor is used to achieve both high energy density and high output characteristics, then the energy density is improved, but the device complexity increases
Solution Approach 1:
The patent combines the energy storage function of the negative electrode (capacitive) with the energy density characteristics of lithium-ion batteries by doping the negative electrode with lithium ions. This merging of functions achieves both high energy density and high output characteristics in a single device structure.
Solution Approach 2:
The negative electrode is designed to perform multiple functions: it serves as both the energy storage electrode (providing capacitive characteristics) and the lithium ion host (providing battery-like energy density). This multi-functionality reduces the need for separate components and simplifies the overall device structure.
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 results in a lithium ion capacitor with high energy and output densities, improved capacity retention during continuous high-temperature charging, and enhanced durability, by forming a stable surface coating film and preventing oxidative decomposition.
Implementation Method 1
Vinylene carbonate or its derivative has a high reductive decomposition potential and dominates the reductive decomposition on the negative electrode and forms a stable and high quality surface coating film
Implementation Method 2
since vinylene carbonate or its derivative has a low oxidation potential, oxidative decomposition on the positive electrode occurs simultaneously
Implementation Method 3
a negative electrode capable of absorbing and desorbing lithium ions is brought into contact with lithium metal so that lithium ions are preliminarily made to be absorbed and supported (hereinafter sometimes referred to as doping) by the negative electrode
Implementation Method 4
after it is assembled, lithium ions are supplied from the lithium-containing metal oxide as the positive electrode to the negative electrode by charging the battery, and the lithium ions in the negative electrode are returned to the positive electrode by discharging the battery
Implementation Method 5
the negative electrode and/or the positive electrode are preliminarily doped with lithium ions by electrochemical contact of the negative electrode and/or the positive electrode with lithium metal as a lithium supply source
Data Source
AI summary
A lithium ion capacitor having a high capacity retention at the time of continuous charge at a high temperature and excellent durability. The lithium ion capacitor includes a positive electrode, a negative electrode and an aprotic organic solvent electrolyte solution of a lithium salt as an electrolytic solution. The positive electrode active material is a material capable of reversibly supporting lithium ions and/or anions, a negative electrode active material is a material capable of reversibly supporting lithium ions, the negative electrode and/or the positive electrode is doped with lithium ions so that the potential of the positive electrode is at most 2.0 V after the positive electrode and the negative electrode are short-circuited, and the electrolytic solution contains vinylene carbonate or its derivative.