Soft Carbon Electrode Prelithiation for Faster SEI Formation
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Solution Overview
Problem
The existing methods for prelithiating soft carbon negative electrodes in lithium-ion capacitors are inefficient, leading to irreversible capacity loss and incomplete formation of the solid electrolyte interphase (SEI), which affects the power density and cycle life of the capacitors.
Innovation Solution
A method involving multiple stages of prelithiation, including a high constant current followed by a lower constant current and then a constant voltage, to ensure complete lithium ion migration and SEI formation, thereby shortening the prelithiation time and improving coulombic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional prelithiation methods are used, then lithium ion capacitors can achieve high working voltages, but the prelithiation process is inefficient leading to irreversible capacity loss and incomplete SEI formation
Solution Approach 1:
The prelithiation process is divided into three distinct stages with different current rates: a first stage at 0.5C rate, a second stage at 0.1C rate, and a third stage at constant voltage. This segmentation allows each stage to optimize for specific aspects of lithium ion migration and SEI formation, improving overall completeness while reducing energy loss.
Solution Approach 2:
The method performs preliminary lithium ion insertion into the soft carbon negative electrode before the capacitor is put into service. By pre-forming the SEI membrane through controlled prelithiation, the system prevents subsequent irreversible capacity loss during normal operation, ensuring complete SEI formation in advance.
2Reliability
If conventional prelithiation methods are used, then lithium ion capacitors can be manufactured, but the prelithiation time is excessively long reducing productivity
Solution Approach 1:
The prelithiation method dynamically adjusts the current rate across three stages: starting at 0.5C for initial lithium ion insertion, reducing to 0.1C for thorough SEI formation, and finishing at constant voltage. This dynamic adjustment optimizes the balance between achieving high coulombic efficiency and reducing total prelithiation time.
Solution Approach 2:
The method changes the electrical parameters (current rate and voltage) across different stages of prelithiation. By transitioning from higher current (0.5C) to lower current (0.1C) and finally to constant voltage, the process achieves complete SEI formation with optimized time requirements, improving both reliability and productivity.
3Power
If asymmetric electrode design is used in lithium ion capacitors, then working voltage increases to approximately 4.0 V, but power density and cycle life depend critically on negative electrode material properties
Solution Approach 1:
The asymmetric lithium ion capacitor uses soft carbon as the negative electrode material and performs preliminary lithium ion insertion before operation. This pre-treatment ensures complete SEI formation on the soft carbon surface, which is critical for achieving both high working voltage (4.0V) and long cycle life, as the SEI membrane protects the negative electrode during subsequent cycling.
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
This method allows for the efficient prelithiation of soft carbon negative electrodes in a significantly shorter time, ensuring stable delithiation curves and high coulombic efficiency, which enhances the performance and longevity of lithium-ion capacitors.
Implementation Method 1
The intercalation/deintercalation of lithium ions in the aforementioned negative electrode materials has a voltage close to 0 V vs. Li/Li+
Implementation Method 2
forms a solid electrolyte interphase (SEI) membrane on the surface of the negative electrode materials
Implementation Method 3
lithium metal in the metal lithium-frame carbon material in the cathode reacts with carbon in the lithium-free active material in the cathode, so that a lithium-carbon compound can be formed
Implementation Method 4
carrying out primary electrochemical charging of the first simple cell dipped in the electrolyte for pre-lithiation to carry out pre-lithiation of the negative electrode
Data Source
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AI summary
A method for prelithiating a soft carbon negative electrode (11) includes the steps of: disposing a lithium-containing electrolyte between the soft carbon negative electrode (11) and a lithium metal piece (12); prelithiating the soft carbon negative electrode (11) at a first constant C-rate until a voltage thereof is reduced to a first predetermined voltage not greater than 0.3 V vs. Li/Li+, the first constant C-rate being not greater than 5 C; prelithiating the soft carbon negative electrode (11) at a second constant C-rate until the voltage thereof is reduced to a second predetermined voltage lower than the first predetermined voltage, the second constant C-rate being not greater than 0.2 C and being less than the first constant C-rate; and prelithiating the soft carbon negative electrode (11) at a prelithiation constant voltage which is not greater than the second predetermined voltage, thereby completing prelithiation of the soft carbon negative electrode (11).