A method for simultaneous pre-lithiation of a reference electrode and a negative electrode, and a lithium-ion capacitor.

Abstract

This invention provides a method for simultaneous pre-lithiation of a reference electrode and a negative electrode, and a lithium-ion capacitor. The method includes assembling a lithium-ion capacitor, electrically connecting the reference electrode in the lithium-ion capacitor to the positive electrode of an external power supply, electrically connecting the negative electrode in the lithium-ion capacitor to the negative electrode of the external power supply, and charging with a constant current to a preset pre-lithiation capacity. The preset pre-lithiation capacity is calculated as follows: Preset pre-lithiation capacity = k × mN × CN; where k is the pre-lithiation coefficient, mN is the mass of the negative electrode active material loaded on the negative electrode (in grams), and CN is the specific capacity of the negative electrode active material (in mAh / g). This invention achieves positive and negative electrode potential monitoring through the design of a lithium iron phosphate reference electrode, simplifying the reference electrode activation and pre-lithiation process into a single step. This allows for simultaneous pre-lithiation of the negative electrode and potential monitoring of both the positive and negative electrodes, improving the manufacturing efficiency and performance of the capacitor.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion capacitor technology, and relates to a method for simultaneous pre-lithiation of a reference electrode and a negative electrode, and a lithium-ion capacitor. Background Technology

[0002] Lithium-ion capacitors, as a novel energy storage device, have received widespread attention from academia and industry in recent years. They combine the high energy density of lithium-ion batteries with the high power density of double-layer capacitors, successfully breaking down the technological barriers between the low energy density of traditional capacitors and the limited power density of batteries. Therefore, lithium-ion capacitors show broad application prospects in fields such as new energy storage (e.g., smoothing wind and photovoltaic power generation output), peak power regulation, industrial energy conservation (e.g., regenerative braking energy recovery), smart grids, and instantaneous high-power power supplies.

[0003] The negative electrode of a lithium-ion capacitor uses battery-grade materials, so a solid electrolyte interphase (SEI) layer also forms on its surface during the first charge. This process consumes lithium ions from the electrolyte, preventing the capacitor from reaching its full usable capacity. Pre-lithiation technology can compensate for the lithium ions lost due to SEI formation, increasing the capacitor's capacity. Pre-lithiation also reduces the potential of the negative and positive electrodes, thereby increasing the operating voltage of the lithium-ion capacitor. This not only helps improve the capacitor's capacity and energy density but also effectively extends its cycle life.

[0004] Despite the numerous advantages of lithium-ion capacitors, the design and research of these capacitors still require independent analysis of the operating potentials of the positive and negative electrodes and their impact on capacitor capacitance, lifespan, and internal resistance. Introducing a reference electrode into the capacitor allows for the separate measurement of the potential and impedance of the positive and negative electrodes relative to the reference electrode, thereby enabling monitoring of the performance of both electrodes during charging and discharging. Lithium metal is a commonly used reference electrode.

[0005] To ensure the high power characteristics of lithium-ion capacitors, polar solvents such as acetonitrile are commonly used as electrolytes. However, acetonitrile reacts violently with lithium metal, making it unsuitable to use lithium metal as a reference electrode for monitoring lithium-ion capacitors containing polar solvents like acetonitrile. Therefore, there is an urgent need to develop a novel reference electrode and pre-lithiation method to overcome the shortcomings of existing technologies and meet practical application requirements. Summary of the Invention

[0006] To address the problems of existing lithium-ion capacitors, such as the difficulty in detecting the positive and negative electrode potentials and the cumbersome pre-lithiation process, this invention provides a method for simultaneous pre-lithiation of the reference electrode and the negative electrode, as well as a lithium-ion capacitor. In this invention, the positive and negative electrode potentials are monitored through the design of a lithium iron phosphate reference electrode. The reference electrode activation and pre-lithiation processes are simplified into a single step; that is, the negative electrode is pre-lithiated simultaneously with the reference electrode activation. This allows for simultaneous pre-lithiation of the negative electrode and monitoring of the potentials of both the positive and negative electrodes, improving the manufacturing efficiency and performance of the capacitor.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a method for simultaneous pre-lithiation of a reference electrode and a negative electrode, the method comprising:

[0009] Assemble a lithium-ion capacitor, electrically connect the reference electrode in the lithium-ion capacitor to the positive terminal of the external power supply, electrically connect the negative electrode in the lithium-ion capacitor to the negative terminal of the external power supply, and charge it with constant current to the preset pre-lithium capacity.

[0010] The preset pre-lithiation capacity is calculated as follows:

[0011] Preset pre-lithiation capacity = k × mN × CN;

[0012] Where k is the pre-lithiation coefficient, mN is the mass of the negative electrode active material loaded on the negative electrode sheet in g, and CN is the specific capacity of the negative electrode active material in mAh / g.

[0013] Furthermore, the value of k ranges from 0.01 to 0.8, for example, it can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Furthermore, the value range of the constant current is 0.5mA to 5mA, for example, it can be 0.5mA, 1mA, 1.5mA, 2mA, 2.5mA, 3mA, 3.5mA, 4mA, 4.5mA, 5mA, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Furthermore, the mass of the active material of the reference electrode in the lithium-ion capacitor, denoted as mR, is calculated as follows:

[0016] mR = preset pre-lithium capacity / (SOC × CR);

[0017] Wherein, SOC is the state of charge of the synchronous pre-lithiation reference electrode, expressed as %, and CR is the specific capacity of the active material of the reference electrode, expressed as mAh / g.

[0018] Furthermore, the value range of SOC is 30% to 70%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] This invention provides a lithium-ion capacitor used in the above-mentioned synchronous pre-lithiation method, the lithium-ion capacitor comprising a casing, a cell, a reference electrode, an electrolyte, and tabs;

[0020] The housing contains the battery cell, the reference electrode, and the electrolyte. The reference electrode is disposed on either side of the battery cell, and the battery cell and the reference electrode are not in direct contact, nor are they indirectly in contact through a diaphragm.

[0021] The battery cell includes a positive electrode plate, a separator, and a negative electrode plate arranged in sequence, and the electrode tabs include a positive electrode tab, a negative electrode tab, and a reference electrode tab;

[0022] The positive electrode tab is connected to the positive electrode plate and extends out of the outer side of the housing; the negative electrode tab is connected to the negative electrode plate and extends out of the outer side of the housing; and the reference electrode tab is connected to the reference electrode and extends out of the outer side of the housing.

[0023] Furthermore, the reference electrode comprises a non-porous aluminum foil and a lithium iron phosphate coating, wherein the lithium iron phosphate coating is disposed on both sides of the non-porous aluminum foil.

[0024] Furthermore, the thickness of the lithium iron phosphate coating is ≤100μm, for example, it can be 100μm, 90μm, 80μm, 70μm, 60μm, 50μm, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Furthermore, the positive electrode sheet includes a positive current collector and a positive electrode material layer coated on the surface of the positive current collector.

[0026] Furthermore, the material of the positive electrode layer includes any one or a combination of two or more of the following: activated carbon, mesoporous carbon, carbon nanotubes, onion carbon, carbon aerogel, activated carbon fiber, skeletal carbon, or graphene.

[0027] Furthermore, the positive current collector is a non-porous aluminum foil.

[0028] Furthermore, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector.

[0029] Furthermore, the material of the negative electrode layer includes any one or a combination of two or more of lithium titanate, lithium niobate, titanium niobium oxide, lithium-containing titanium niobium oxide, niobium pentoxide, titanium dioxide, hard carbon, soft carbon, graphite, mesophase carbon microspheres, or silicon suboxide.

[0030] Furthermore, the negative electrode current collector is a non-porous aluminum foil or a non-porous copper foil.

[0031] Furthermore, the electrolyte comprises a lithium-containing electrolyte salt and a solvent.

[0032] Furthermore, the lithium-containing electrolyte salt includes any one or a combination of two or more of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis-trifluoromethanesulfonylimide, or lithium bisfluorosulfonylimide.

[0033] Further, the solvent includes any one or a combination of two or more of acetonitrile, ethyl acetate, γ-butyrolactone, sulfolane, adiponitrile, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, or ethyl isopropyl sulfone.

[0034] Furthermore, the injected electrolyte mass is 1.5 times or more of the saturated electrolyte mass of the battery cell, for example, it can be 1.5 times, 1.7 times, 2 times, 3 times, 4 times, 5 times, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] In this invention, lithium iron phosphate can exist stably in air, avoiding the need to fabricate the reference electrode in a glove box, eliminating cumbersome experimental steps, and making it easy to manufacture. At the same time, by using the reference electrode, the state changes of the positive and negative electrodes can be directly monitored, enabling effective differentiation of their electrochemical behavior.

[0038] This invention employs an in-situ lithiation method, charging the negative electrode to a preset pre-lithiation capacity using a reference electrode with a constant current. This enables non-destructive analysis of the life decay mechanism of lithium-ion capacitors without disassembling the capacitors. It allows direct monitoring of the state changes of the positive and negative electrodes, effectively distinguishing the electrochemical behavior of the positive and negative electrodes, thus achieving non-destructive analysis of the life decay mechanism of lithium-ion capacitors.

[0039] In this invention, the pre-lithiation of the negative electrode is achieved simultaneously while the reference electrode is activated, simplifying the reference electrode activation and pre-lithiation process into one step. There is no need to pre-activate the reference electrode before implanting the lithium-ion capacitor, nor is it necessary to disassemble the lithium-ion capacitor after pre-lithiation to remove the pre-lithiated lithium source. This greatly simplifies the manufacturing process of lithium-ion capacitors and improves production efficiency.

[0040] In this invention, the reference electrode and the battery cell are relatively independent. The reference electrode will not interfere with the normal electrochemical reaction of the lithium-ion capacitor, thereby improving the stability and reliability of the lithium-ion capacitor. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 A schematic diagram of the structure of a lithium-ion capacitor provided in one embodiment of the present invention;

[0043] Figure 2 The charge-discharge test curve of the lithium-ion capacitor in Embodiment 1 of the present invention;

[0044] Figure 3 The charge-discharge test curve of the lithium-ion capacitor in Embodiment 2 of the present invention;

[0045] Among them, 101-shell, 102-cell, 103-reference electrode, 104-reference tab; 105-positive tab, 106-negative tab. Detailed Implementation

[0046] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0047] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0048] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0050] In one embodiment, the present invention provides a method for simultaneous pre-lithiation of a reference electrode and a negative electrode, the method comprising:

[0051] Assemble a lithium-ion capacitor, electrically connect the reference electrode 103 in the lithium-ion capacitor to the positive terminal of the external power supply, electrically connect the negative electrode in the lithium-ion capacitor to the negative terminal of the external power supply, and charge it with constant current to the preset pre-lithium capacity.

[0052] The preset pre-lithiation capacity is calculated as follows:

[0053] Preset pre-lithiation capacity = k × mN × CN;

[0054] Where k is the pre-lithiation coefficient, mN is the mass of the negative electrode active material loaded on the negative electrode sheet in g, and CN is the specific capacity of the negative electrode active material in mAh / g.

[0055] It should be noted that the one-step pre-lithiation of the reference electrode 103 and the negative electrode in this invention includes charging the negative electrode of the assembled lithium-ion capacitor to a preset pre-lithiation capacity through the reference electrode 103 with a current of 0.5~5mA. The preset pre-lithiation capacity of the reference electrode 103 is 30~70% of the theoretical capacity. The activation of the reference electrode 103 and the one-step pre-lithiation of the negative electrode are the same step. The reference electrode 103 is activated while the negative electrode is pre-lithiated. The activation of the reference electrode 103 and the pre-lithiation of the negative electrode are combined into one step, which simplifies the process.

[0056] In some implementations, the value of k ranges from 0.01 to 0.8, for example, it can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] In this invention, the value of k ranges from 0.01 to 0.8 because this range is the design value for cell 102, and it can be selected within this range according to the actual situation. If it exceeds this value, it will generally cause the negative electrode potential to be too low when the lithium-ion capacitor is charged to the maximum voltage, resulting in problems such as lithium plating on the negative electrode or damage to the negative electrode material, which will affect the life of the lithium-ion capacitor. If it is lower than this value, the reference electrode 103 cannot be effectively activated.

[0058] In some implementations, the constant current ranges from 0.5mA to 5mA, for example, it can be 0.5mA, 1mA, 1.5mA, 2mA, 2.5mA, 3mA, 3.5mA, 4mA, 4.5mA, 5mA, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0059] In this invention, the constant current ranges from 0.5mA to 5mA. If it exceeds this value, it will generally lead to difficulty in uniform pre-lithiation of the negative electrode and the voltage of the pre-lithiation process will be too high. If it is lower than this value, the activation of the reference electrode 103 and the synchronous pre-lithiation process of the negative electrode will take too long, reducing efficiency.

[0060] In some embodiments, the mass of the active material of the reference electrode 103 in the lithium-ion capacitor, denoted as mR, is calculated as follows:

[0061] mR = preset pre-lithium capacity / (SOC × CR);

[0062] Wherein, SOC is the state of charge of the reference electrode 103 after synchronous pre-lithiation, in %; CR is the specific capacity of the active material of the reference electrode 103, in mAh / g.

[0063] It should be noted that in this invention, the calculation is based on the formula mR = preset pre-lithium capacity / (SOC × CR), meaning that the quality of the active material of the reference electrode 103 needs to be precisely controlled in order to keep the SOC within 30% to 70%.

[0064] In some embodiments, the SOC value of the reference electrode 103 is in the range of 30% to 70%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0065] In this invention, the SOC value ranges from 30% to 70% because the potential of the reference electrode 103 is stable within this range. If the value exceeds or falls below this value, the potential of the reference electrode 103 will fluctuate, and the potential of the positive and negative electrodes cannot be effectively monitored.

[0066] In one specific embodiment, the present invention provides a lithium-ion capacitor used in the above-described synchronous pre-lithiation method, such as... Figure 1 As shown, it includes a housing 101, a battery cell 102, a reference electrode 103, an electrolyte, and tabs;

[0067] The housing 101 contains a battery cell 102, a reference electrode 103 and an electrolyte. The reference electrode 103 is disposed on either side of the battery cell 102, and the battery cell 102 and the reference electrode 103 are not in direct contact, nor are they indirectly in contact through a diaphragm.

[0068] The battery cell 102 includes a positive electrode plate, a separator and a negative electrode plate arranged in sequence, and the tabs include a positive electrode tab 105, a negative electrode tab 106 and a reference electrode tab 104;

[0069] The positive electrode tab 105 is connected to the positive electrode plate and extends out of the outer side of the housing 101; the negative electrode tab 106 is connected to the negative electrode plate and extends out of the outer side of the housing 101; and the reference electrode tab 104 is connected to the reference electrode 103 and extends out of the outer side of the housing 101.

[0070] It should be noted that the assembly of lithium-ion capacitors in this invention includes stacking positive electrode plates, separators and negative electrode plates to form a cell 102, assembling the cell 102 and reference electrode 103 into a shell, vacuum drying, and injecting a certain amount of electrolyte, thereby obtaining the assembled lithium-ion capacitor with lithium iron phosphate reference electrode 103.

[0071] In some embodiments, the reference electrode 103 includes a non-porous aluminum foil and a lithium iron phosphate coating, wherein the lithium iron phosphate coating is disposed on both sides of the non-porous aluminum foil.

[0072] In some embodiments, the thickness of the lithium iron phosphate coating is ≤100μm, for example, it can be 100μm, 90μm, 80μm, 70μm, 60μm, 50μm, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0073] In this invention, the thickness of the lithium iron phosphate coating is ≤100μm. If it exceeds this value, it will generally lead to excessive polarization of the reference electrode 103 activation and the synchronous pre-lithiation of the negative electrode, making it difficult for the negative electrode to be uniformly pre-lithiated, and the voltage of the pre-lithiation process will be too high.

[0074] In some embodiments, the positive electrode includes a positive current collector and a positive electrode material layer coated on the surface of the positive current collector.

[0075] In some embodiments, the cathode material layer is made of any one or a combination of two or more of activated carbon, mesoporous carbon, carbon nanotubes, onion carbon, carbon aerogel, activated carbon fiber, skeletal carbon, or graphene.

[0076] In some implementations, the positive current collector is a non-porous aluminum foil.

[0077] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode material layer coated on the surface of the negative current collector.

[0078] In some embodiments, the material of the negative electrode layer includes any one or a combination of two or more of lithium titanate, lithium niobate, titanium niobium oxide, lithium-containing titanium niobium oxide, niobium pentoxide, titanium dioxide, hard carbon, soft carbon, graphite, mesophase carbon microspheres, or silicon suboxide.

[0079] In some embodiments, the negative current collector is a non-porous aluminum foil or a non-porous copper foil.

[0080] In some embodiments, the electrolyte includes a lithium-containing electrolyte salt and a solvent.

[0081] In some embodiments, the lithium-containing electrolyte salt includes any one or a combination of two or more of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis-trifluoromethanesulfonylimide, or lithium bisfluorosulfonylimide.

[0082] In some embodiments, the solvent includes any one or a combination of two or more of acetonitrile, ethyl acetate, γ-butyrolactone, sulfolane, adiponitrile, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, or ethyl isopropyl sulfone.

[0083] In some embodiments, the injected electrolyte mass is 1.5 times or more of the saturated electrolyte mass of the cell 102, for example, it can be 1.5 times, 1.7 times, 2 times, 3 times, 4 times, 5 times, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0084] It should be noted that the amount (mass) of electrolyte injected in this invention is more than 1.5 times the saturated electrolyte absorption capacity of the cell 102. The main reason why the amount of electrolyte injected greatly exceeds the saturated electrolyte absorption capacity of the cell 102 is that the reference electrode 103 is set on the upper or lower side of the cell 102. The reference electrode 103 and the cell 102 are relatively independent and are not placed opposite each other. The reference electrode 103 and the cell 102 are not in close contact and do not form direct contact, nor do they form indirect contact through the insulation of the diaphragm. An electrical connection needs to be formed through the electrolyte as a medium. When the electrolyte is too little, the reference electrode 103 and the cell 102 are insulated or have a large internal resistance, making it difficult to perform negative electrode pre-lithiation and positive and negative electrode potential monitoring.

[0085] It should be noted that, in this invention, the saturated electrolyte absorption of cell 102 refers to the amount of electrolyte required to fill the pore volume of the positive electrode, negative electrode, and separator in cell 102.

[0086] Example 1

[0087] This embodiment provides a method for simultaneous pre-lithiation of a reference electrode 103 and a negative electrode, wherein:

[0088] Assemble a lithium-ion capacitor, electrically connect the reference electrode 103 in the lithium-ion capacitor to the positive terminal of the external power supply, electrically connect the negative electrode in the lithium-ion capacitor to the negative terminal of the external power supply, and charge it with a constant current of 2mA to the preset pre-lithium capacity.

[0089] The preset pre-lithiation capacity is calculated as follows:

[0090] Preset pre-lithiation capacity = k × mN × CN;

[0091] Where k is 0.5, mN is 2.0g (unit: g), and CN is 200mAh / g.

[0092] The mass of the active material of the reference electrode 103 in the lithium-ion capacitor, denoted as mR, is calculated as follows:

[0093] mR = preset pre-lithium capacity / (SOC × CR);

[0094] The SOC is 50% and the CR is 155mAh / g.

[0095] The lithium-ion capacitor in this embodiment includes a housing 101, a battery cell 102, a reference electrode 103, an electrolyte, and tabs. The battery cell 102 includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The reference electrode 103 is disposed on the upper side of the battery cell 102. The positive electrode tab 105 is connected to the positive electrode and extends out of the housing 101, the negative electrode tab 106 is connected to the negative electrode and extends out of the housing 101, and the reference electrode tab 104 is connected to the reference electrode 103 and extends out of the housing 101.

[0096] The positive electrode active material is activated carbon, and the positive electrode current collector is aluminum foil; the negative electrode active material is niobium pentoxide, and the negative electrode current collector is aluminum foil; the active material of the reference electrode 103 is lithium iron phosphate, the thickness of the lithium iron phosphate coating is 50 μm, and the current collector of the reference electrode 103 is aluminum foil. The electrolyte solvent is acetonitrile, and the lithium-containing electrolyte salt is lithium tetrafluoroborate.

[0097] Lithium-ion capacitor assembly: The positive electrode, separator and negative electrode are stacked to form a cell 102. The cell 102 and reference electrode 103 are assembled into a shell, vacuum dried, and injected with electrolyte (30g) three times the saturated liquid absorption capacity of the cell 102, thereby obtaining the assembled lithium-ion capacitor with lithium iron phosphate reference electrode.

[0098] The assembled lithium-ion capacitor charges the negative electrode to 200 mA through the reference electrode 103 with a current of 2 mA.

[0099] Figure 2 The above are the charge / discharge test curves of the lithium-ion capacitor in this embodiment. The test current is 0.2A, and the test voltage range is 1.0~2.7V. Curve A is the voltage curve between the positive and negative electrodes, curve B is the potential of the positive electrode relative to the lithium iron phosphate reference electrode, and curve C is the potential of the negative electrode relative to the lithium iron phosphate reference electrode.

[0100] The positive electrode potential range is -0.69~0.86V relative to the lithium iron phosphate electrode, and the negative electrode potential range is -1.84~-1.69V relative to the lithium iron phosphate electrode.

[0101] Example 2

[0102] This embodiment provides a method for simultaneous pre-lithiation of a reference electrode 103 and a negative electrode. The difference from Embodiment 1 is that the pre-lithiation coefficient k is 0.02, therefore, the pre-lithiation capacity is 8mAh, the mass mR of the active material of the reference electrode 103 is 0.1g, and the assembled lithium-ion capacitor charges the negative electrode to 8mAh through the reference electrode 103 with a current of 2mA.

[0103] Figure 3The above are the charge / discharge test curves of the lithium-ion capacitor in this embodiment. The test current is 0.2A, and the test voltage range is 1.0~2.7V. Among them, curve D is the voltage curve between the positive and negative electrodes, curve E is the potential of the positive electrode relative to the lithium iron phosphate reference electrode, and curve F is the potential of the negative electrode relative to the lithium iron phosphate reference electrode.

[0104] The positive electrode potential range is -0.31 to 1.08V relative to the lithium iron phosphate electrode, and the negative electrode potential range is -1.62 to -1.31V relative to the lithium iron phosphate electrode.

[0105] Comparative Example 1

[0106] The difference between this comparative example and Example 1 is that the reference electrode 103 is made of lithium metal. During the assembly of a lithium-ion capacitor, after the electrolyte is injected, a violent reaction occurs between the lithium metal and the acetonitrile solvent in the electrolyte, causing an explosion.

[0107] Comparative Example 2

[0108] The difference between this comparative example and Example 1 is that 10g of electrolyte was injected. Due to the insufficient amount of electrolyte, the reference electrode 103 and the cell 102 were either insulated or had high internal resistance, and an effective electrical connection could not be formed between the reference electrode 103 and the cell 102. As a result, the activation of the reference electrode 103 and the pre-lithiation of the negative electrode failed.

[0109] Comparative Example 3

[0110] The difference between this comparative example and Example 1 is that the mass mR of the active material of the reference electrode 103 is 15g. Because the mass of the reference electrode 103 is too large, after activation with a pre-lithiation capacity of 200mAh, the reference electrode 103 was not in a stable state, and its potential fluctuated significantly, affecting the accuracy of the positive and negative electrode potential measurements.

[0111] Comparative Example 4

[0112] The difference between this comparative example and Example 1 is that the mass mR of the active material of the reference electrode 103 is 1.5g. Because the mass of the reference electrode 103 is too small, after activation with a pre-lithiation capacity of 200mAh, the reference electrode 103 is not in a stable state, and its potential fluctuates significantly, affecting the accuracy of positive and negative electrode potential measurements.

[0113] Comparative Example 5

[0114] The difference between this comparative example and Example 1 is that the mass mR of the active material of the reference electrode 103 is 1.0 gram. The mass of the reference electrode 103 is too small, the pre-lithiation capacity fails to reach the designed 200 mAh for lithium-ion capacitors, the reference electrode 103 is not in a stable state, and the potential fluctuation of the reference electrode 103 is large, affecting the accuracy of positive and negative electrode potential measurements.

[0115] In summary, this invention achieves positive and negative electrode potential monitoring through the design of a lithium iron phosphate reference electrode. The activation and pre-lithiation process of the reference electrode 103 is simplified into one step, that is, the pre-lithiation of the negative electrode is achieved simultaneously with the activation of the reference electrode 103, so as to simultaneously achieve the pre-lithiation of the negative electrode and the potential monitoring of the positive and negative electrodes of the lithium-ion capacitor, thereby improving the manufacturing efficiency and performance of the capacitor.

[0116] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for simultaneous pre-lithiation of a reference electrode and a negative electrode, characterized in that, The simultaneous pre-lithiation method includes: Assemble a lithium-ion capacitor, electrically connect the reference electrode in the lithium-ion capacitor to the positive terminal of the external power supply, electrically connect the negative electrode in the lithium-ion capacitor to the negative terminal of the external power supply, and charge it with constant current to the preset pre-lithium capacity. The preset pre-lithiation capacity is calculated as follows: Preset pre-lithiation capacity = k × mN × CN; Where k is the pre-lithiation coefficient, mN is the mass of the negative electrode active material loaded on the negative electrode sheet in g, and CN is the specific capacity of the negative electrode active material in mAh / g. The value of k ranges from 0.01 to 0.8; The mass of the active material of the reference electrode in the lithium-ion capacitor, denoted as mR, is calculated as follows: mR = preset pre-lithium capacity / (SOC × CR); Wherein, SOC is the state of charge of the reference electrode after simultaneous pre-lithiation, in %; CR is the specific capacity of the active material of the reference electrode, in mAh / g. The SOC value ranges from 30% to 70%. The reference electrode is made of lithium iron phosphate.

2. The simultaneous pre-lithiation method according to claim 1, characterized in that, The constant current ranges from 0.5mA to 5mA.

3. A lithium-ion capacitor used in the synchronous pre-lithiation method as described in claim 1 or 2, characterized in that, The lithium-ion capacitor includes a casing, a battery cell, a reference electrode, an electrolyte, and tabs. The housing contains the battery cell, the reference electrode, and the electrolyte. The reference electrode is disposed on either side of the battery cell, and the battery cell and the reference electrode are not in direct contact, nor are they indirectly in contact through a diaphragm. The battery cell includes a positive electrode plate, a separator, and a negative electrode plate arranged in sequence, and the electrode tabs include a positive electrode tab, a negative electrode tab, and a reference electrode tab; The positive electrode tab is connected to the positive electrode plate and extends out of the outer side of the housing; the negative electrode tab is connected to the negative electrode plate and extends out of the outer side of the housing; and the reference electrode tab is connected to the reference electrode and extends out of the outer side of the housing.

4. The lithium-ion capacitor according to claim 3, characterized in that, The reference electrode comprises a non-porous aluminum foil and a lithium iron phosphate coating, wherein the lithium iron phosphate coating is disposed on both sides of the non-porous aluminum foil; The thickness of the lithium iron phosphate coating is ≤100μm.

5. The lithium-ion capacitor according to claim 3, characterized in that, The positive electrode sheet includes a positive current collector and a positive electrode material layer coated on the surface of the positive current collector; The material of the positive electrode layer includes any one or a combination of two or more of the following: activated carbon, mesoporous carbon, carbon nanotubes, onion carbon, carbon aerogel, activated carbon fiber, skeletal carbon, or graphene. The positive current collector is a non-porous aluminum foil.

6. The lithium-ion capacitor according to claim 3, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector; The material of the negative electrode layer includes any one or a combination of two or more of the following: lithium titanate, lithium niobate, titanium niobium oxide, lithium-containing titanium niobium oxide, niobium pentoxide, titanium dioxide, hard carbon, soft carbon, graphite, mesophase carbon microspheres, or silicon suboxide. The negative electrode current collector is a non-porous aluminum foil or a non-porous copper foil.

7. The lithium-ion capacitor according to claim 3, characterized in that, The electrolyte comprises a lithium-containing electrolyte salt and a solvent; The lithium-containing electrolyte salt includes any one or a combination of two or more of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate, lithium bis-trifluoromethanesulfonylimide, or lithium bisfluorosulfonylimide. The solvent includes any one or a combination of two or more of the following: acetonitrile, ethyl acetate, γ-butyrolactone, sulfolane, adiponitrile, ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, or ethyl isopropyl sulfone. The injected electrolyte mass is 1.5 times or more of the saturated electrolyte mass of the battery cell.

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