Metal-ion capacitor based on hard carbon as negative electrode and a mixture of activated carbon and sacrificial salt as positive electrode

Abstract

The present invention relates to a metal-ion capacitor with outstanding power performance, which includes a negative electrode based on hard carbon (HC) and a positive electrode based on a combination of activated carbon (AC) and a sacrificial salt selected from the group consisting of squarates, oxalates, ketomalonates, and diketosuccinates, or combinations thereof. The sacrificial salt is added to the AC at the positive electrode as a metal ion source for pre-doping the HC and efficiently supplementing its high irreversible capacity by providing the metal ions necessary for the formation of a solid electrolyte interphase (SEI) on the hard carbon, enabling excellent 1:1 mass balance between the anode and cathode. Advantageously, the outstanding performance of this approach has been successfully demonstrated not only in lithium-ion capacitors (LICs), but also in other metal-ion capacitors, such as sodium and potassium-ion capacitors.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical energy storage, and more particularly to metal-ion capacitors (MICs) that exhibit both high energy and high power density.

Background Art

[0002] In recent years, in response to the increasing demand for high-energy density transmission at high power, considerable research has been intensively conducted on electrochemical energy storage. On the one hand, batteries such as lithium-ion batteries (LIBs) rely on Faradaic reactions that can provide very high energy densities, but such batteries are limited in terms of power and cyclability. In contrast, supercapacitors store charge by capacitive reactance that enables high power and long cyclability at the expense of energy density. Recently, metal-ion capacitors (MICs), specifically those based on lithium ions, have emerged as a combined solution that has the potential to provide high energy density at high power density with long cyclability by integrating the aforementioned technologies using battery-grade electrodes paired with capacitor-type electrodes. Among the various lithium-ion capacitors (LICs) developed in recent years, dual-carbon-based LICs are promising even in commercially available products (ULTIMO (registered trademark)). Nevertheless, the commercialization of this type of system is hindered by irreversible losses of charge (e-) and active lithium (Li+) during cycling that affect Coulombic and energy efficiency. The main mechanism currently recognized is said to be due to the formation of a solid electrolyte interphase (SEI) on the negative electrode during the first charge. Therefore, a so-called prelithiation process to compensate for this Li+ (and electron) loss is necessary for the full utilization of the active material. This is one of the major issues to be considered in the manufacture of high-efficiency LIBs and LICs. It should be noted that this major issue is common to both LIBs and LICs, but prelithiation is even more important for LICs because any additional Li+ ion source must not only address SEI formation but also be large enough to lithiate the negative electrode (during charging). Therefore, the prelithiation of carbon in LICs remains a major technical barrier. Therefore, commercially available LICs are currently based on anodes made of graphite, which, despite its slow reaction rate, exhibits lower first-cycle irreversibility than other carbonaceous materials such as hard carbon and provides an easier prelithiation solution.

[0003] For many years, several techniques have been used at LIC to prelithiate graphite. Fuji Co. has proposed an approach currently used in the industry (ULTIMO (registered trademark), JM Energy) that uses a lithium foil as a third electrode to prelithiate a graphite anode electrode. This LIC structure results in an electrochemical energy storage device having three electrodes (a cathode, an anode, and a sacrificial lithium metal electrode). This three-electrode LIC requires the use of a mesh-type current collector for both the cathode and the anode to enable the transport of lithium ions into and between the cathode and the anode, which complicates and increases the cost of manufacturing the cell design. Further, it reintroduces the risks associated with early lithium-ion batteries based on the use of metallic lithium, such as the risk of short circuit and thermal runaway. Alternatively, electrochemical prelithiation can be performed in a separate cell. However, in many cases, the electrochemical prelithiation process requires the reassembly step of the prelithiated negative electrode into the LIC cell under an inert atmosphere, which increases costs and reduces the likelihood of using this method in a commercial manner.

[0004] As a result, alternative cost-effective prelithiation strategies have been developed in recent years. One of the most widespread approaches is the use of a composite cathode. Lithiated metal oxides are incorporated into the positive electrode and combined with activated carbon as an irreversible lithium source. Metal oxides such as Li 2 MoO 3 、Li 5 FeO 6 or Li 2 RuO 3 have been proposed. Still, this approach presents several challenges to be addressed for its implementation as a viable solution for prelithiation. First, the lithium extraction potential of most of these metal oxides promotes electrolyte decomposition, which negatively affects the subsequent LIC cyclability, at 4.7V vs. Li / Li +Higher. Next, the decomposed metal oxides remain as dead mass in the cell, disadvantaging the energy density. Finally, the high cost of metal oxides has an adverse impact on the price of the entire final product. To address this problem, in very recent years, the sacrificial salt concept has been adopted from lithium-ion battery (LIB) technology. Carbonyl-based organic compounds are mixed with activated carbon at the positive electrode. Lithium is incorporated into the structure of the organic compounds such that they can be irreversibly oxidized (i.e., lithium extraction). Since the organic compounds are highly insulating and require a large amount of conductive carbon to decompose, it is a composite mixture and a drawback in LIB technology not present in LICs as the active material is already highly conductive carbon. Jezowski et al. (Safe and recyclable lithium-ion capacitors using sacrificial organic lithium salt, Nature materials, 2017, 1-7) developed this approach for the first time by synthesizing a 3,4-dihydroxybenzonitrile dilithium salt with a de-lithiation potential of 3.5 V vs Li / Li + and a high theoretical capacity of 365 mAh / g that can fully prelithiate a graphite electrode. The resulting quinone oxide is soluble, which leads to a shuttle mechanism. Furthermore, the developed LICs lack high power, which is hindered by the use of graphite.

[0005] Due to the high irreversibility of the first cycle, hard carbon is excluded from the above-mentioned prelithiation solutions and has received much less attention. From the perspective of its high irreversible capacity, hard carbon requires a very high degree of prelithiation. Therefore, the prelithiation of hard carbon-based anodes has always been addressed by using lithium metal, which provides an almost infinite supply of lithium ions. In this regard, Zheng et al. developed prelithiation for hard carbon by using metallic lithium in different forms. First, stabilized lithium metal powder (SLMP) was used to successfully prelithiate hard carbon. Nevertheless, despite the stabilization of lithium, it remains highly reactive, leading to safety issues that are not suitable for industrial-scale manufacturing. An alternative approach was also developed by the same group using a lithium metal strip in direct contact with the electrolyte. Again, hard carbon was successfully prelithiated, but the use of metallic lithium and the complexity of the approach hinder its industrialization. See Zheng et al., Constructing High Energy and Power Densities Li-Ion Capacitors Using Li Thin Film for Pre-Lithiation, Journal of The Electrochemical Society, 2017, 164, A2164-A2170.

[0006] Therefore, there is still a need to develop new electrochemical energy storage solutions that overcome the limitations of the above systems. SUMMARY OF THE INVENTION

[0007] The present invention addresses the limitations of the prior art by providing a metal-ion capacitor (MIC) based on a hard carbon anode with remarkable power performance. In particular, the inventors have found that sacrificial salts, when added to activated carbon (AC) in the positive electrode as a metal-ion source, can efficiently compensate for the high irreversible capacity of the hard carbon (HC) anode and enable an excellent mass balance of 1:1 between the anode and the cathode. Advantageously, the remarkable performance of this approach has been successfully demonstrated not only in lithium-ion capacitors (LICs) but also in other metal-ion capacitors such as sodium and potassium ion capacitors. Furthermore, the MIC described herein is compatible with an industrial and easily scalable manufacturing process that enables an increase in energy and targets a higher power than that of graphite-based capacitors, allowing the use of HC as the negative electrode in the MIC.

[0008] In one aspect, the present invention relates to - a negative electrode comprising hard carbon, - a positive electrode comprising activated carbon and a sacrificial salt, and - a separator positioned between the two electrodes, wherein the sacrificial salt is selected from the group consisting of squarate, oxalate, ketomalonate, and dike to succinate or combinations thereof, for a metal-ion capacitor.

[0009] During operation, an electrolyte solution can be incorporated throughout the cathode, anode, and separator. The electrolyte solution contains an electrolyte material (solute) dissolved in a solvent.

[0010] In another aspect, the present invention relates to a method for manufacturing the metal-ion capacitor described herein, the method comprising the fabrication of the negative hard carbon electrode and / or the activated carbon of the positive electrode from biomass waste.

[0011] In another aspect, the present invention is the use of a sacrificial salt as a metal ion source for pre-doping the negative electrode of a metal ion capacitor and for supplementing the requirements of metal ions for forming a solid electrolyte interphase (SEI) on the negative electrode, the sacrificial salt being combined with activated carbon at the positive electrode, the sacrificial salt being selected from the group consisting of squarates, oxalates, ketomalonates and diketosuccinates or combinations thereof, and the negative electrode comprising hard carbon, for use.

[0012] Furthermore, this aspect and its preferred embodiments are also defined below in the detailed description and claims.

Brief Description of the Drawings

[0013] For a more complete understanding of the present invention, its objects and advantages, the following drawings are appended to the specification.

[0014]

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MODE FOR CARRYING OUT THE INVENTION

[0015] Current alkali metal ion capacitor technologies, for example, lithium ion capacitors (LICs), are based on dual carbon electrode systems, and graphite is the most commonly used material at the negative electrode. Since the positive electrode is not a lithium source and all lithium must originate from a prelithiation source, a higher degree of prelithiation is required for LICs compared to lithium ion batteries (LIBs). Therefore, currently, graphite is used as the negative electrode. This is because its irreversible capacity is as low as only about 5%, thus minimizing the amount of lithium required in the prelithiation process. Nevertheless, the slow reaction rate of graphite limits LIC technology from a power perspective, and the use of a more powerful material at the negative electrode is highly desirable. Furthermore, the technology must also be applicable to other metal ion capacitors such as sodium and potassium ion capacitors in addition to LICs.

[0016] The solution provided by the present invention is - at least one anode comprising hard carbon (HC), - at least one cathode comprising activated carbon (AC) and a sacrificial salt selected from the group consisting of squarate, oxalate, ketomalonate and dike to succinate or combinations thereof, and - A metal ion capacitor including a separator interposed between two electrodes.

[0017] The electrodes, anode and cathode are preferably immersed in an electrolyte solution or positioned in some other way together with the separator interposed therebetween.

[0018] The anode is made of hard carbon. As used herein, the HC material preferably has a specific surface area of less than about 500 m 2 / g, for example less than about 100 m 2 / g. In embodiments, the HC material used to form the anode is not graphitizable and preferably may have an average particle size of less than about 100 microns, such as less than about 100, about 10, about 5 or about 1 micron, or equal to about 1 micron. In a more preferred embodiment, the HC material has an average particle size in the range of about 0.1 to about 5 microns, such as about 0.5 to about 2 microns, or more specifically about 1 micron. Surprisingly, good performance can be achieved even with a small particle size. The thickness of the anode containing HC can be in the range of, for example, about 25 to about 600 microns.

[0019] The cathode is made of a composite material containing activated carbon and a sacrificial salt. As used herein, the AC material preferably has a specific surface area greater than about 500 m 2 / g. In embodiments, the AC material used to form the cathode preferably may have an average particle size of less than 100 microns, such as less than about 100, about 10 or about 5 microns. The thickness of the cathode containing AC / sacrificial salt can be in the range of, for example, about 25 to about 600 microns.

[0020] According to the present invention, HC and AC, which function as an anode and a cathode, respectively, can be synthesized from various precursors such as sucrose, cellulose, polyvinyl (PVC), furfuryl alcohol, or even better ones, from sustainable resources such as recycled biomass. In a preferred embodiment, the carbon material is made from biomass waste such as coconut shells, peanut shells, fruit peels, olive seeds, etc. Of course, a combination of two or more precursors may be employed to produce the carbon of the present invention. In a particularly preferred embodiment, HC and AC are synthesized from recycled olive seeds.

[0021] Generally, the production of HC involves heating a carbon precursor at a high temperature of at least about 30 minutes (e.g., about 30 - 240 minutes), usually about 600 °C or higher (e.g., about 600 - 1800 °C, about 650 - 1500 °C, about 700 - 1200 °C, or about 750 - 1000 °C) in an inert atmosphere (e.g., Ar flow) to pyrolyze the precursor. In the case of a solid, the carbon precursor can be pulverized before pyrolysis. In certain cases, the temperature increases gradually (e.g., at a ramp rate of about 2 - 10 °C / min) until the pyrolysis temperature is reached.

[0022] According to a detailed embodiment, HC is produced from biomass waste (e.g., olive seeds) by a process that includes heating the preferably pre - pulverized biomass waste at a ramp rate of about 3 - 8 °C / min to a predetermined temperature in the range of about 600 - 1800 °C (e.g., about 750 - 1000 °C) and further holding it for about 1.5 - 2.5 hours. In a more detailed embodiment, the biomass waste is heated at a ramp rate of about 4 - 6 °C / min (e.g., under an Ar flow of about 50 - 250 ml / min) to a predetermined temperature in the range of about 750 - 1000 °C (e.g., about 800 °C) and further holding it for about 1.5 - 2.5 hours, by which the pyrolysis process is pulverized and filled in a furnace (e.g., a tubular furnace).

[0023] Next, to adjust the particle size and prepare HC for high-power applications, the HC can be mechanically ground and pulverized. In a detailed embodiment, after pyrolysis, the HC is then manually coarsely ground in a mortar / pestle before being pulverized in a ball mill in a planetary mill. The pulverization can be carried out for about 60 - 120 minutes.

[0024] Activated carbon (AC) can be made from pre-obtained hard carbon (HC) (without being mechanically ground and pulverized). Generally, to make activated carbon (AC), the pre-obtained hard carbon (HC) (without a grinding and ball milling process) can usually be physically mixed with a hydroxide such as potassium hydroxide in various mass ratios of about 1:1 or more (e.g., about 1:10, about 1:8, about 1:6, about 1:4 or about 1:2). Then, the HC mixed with the hydroxide can be activated by heating to a temperature of about 600 - 800 °C (e.g., about 650 °C, about 700 °C, about 750 °C) under an inert atmosphere (e.g., Ar flow). In an embodiment, the material mixture is placed in a boat and heated to a temperature of about 600 - 800 °C (e.g., about 650 °C, about 700 °C, about 750 °C) under an inert atmosphere (e.g., an Ar flow of about 50 - 250 ml / min) inside a furnace (e.g., a tubular furnace), preferably inside a horizontal stainless steel tube, to be activated. In certain cases, the temperature increases gradually (e.g., at a ramp rate of about 2 - 10 °C / min). The holding time at the determined temperature can usually be set to about 30 minutes to about 5 hours (e.g., about 1 - 2 hours, about 2 - 3 hours, about 3 - 4 hours, about 4 - 5 hours). After activation, the microporous AC can be washed and dried to a neutral pH. For example, the microporous AC can be washed with a dilute solution of acid and water until it reaches a neutral pH and then dried, preferably under vacuum, at about 100 - 150 °C.

[0025] According to a detailed embodiment, AC is prepared by physically mixing the pre-obtained HC with potassium hydroxide at a mass ratio of about 1:5 to 1:7. The mixed material is placed in a boat (e.g., an Inconel® boat) and activated by heating to about 650 - 750 °C under an Ar flow of about 50 - 250 ml / min inside a horizontal stainless steel tube in a tubular furnace. The temperature is gradually increased at a ramp rate of about 3 - 8 °C / min, and the holding time at the determined temperature is set to about 1.5 - 2.5 hours. After activation, the microporous AC is washed with a dilute solution of hydrochloric acid and water until it reaches a neutral pH, and then dried at about 120 °C under vacuum.

[0026] AC is combined with a sacrificial salt at the cathode of the metal ion capacitor of the present invention. The sacrificial salt functions as a metal ion source for pre-doping the negative electrode and for supplementing the requirement of metal ions for forming a solid electrolyte interphase (SEI) on the negative electrode. More specifically, the term "sacrificial salt" refers to a metal salt that can release metal ions and decompose during the first charge so that metal ions can be charged into the negative electrode and the loss of active metal ions due to SEI formation can be compensated. That is, the sacrificial salt can supply metal ions into the structure of HC and further compensate for its high irreversible capacity by providing the metal ions necessary for the formation of an inactivated layer on the surface of the negative electrode.

[0027] Sacrificial salts useful in the present invention include squarates, oxalates, ketomalonates, and diketosuccinates or combinations thereof. The metal of the sacrificial salt is preferably selected from metal ions with a +1 charge such as alkali metals. The chemical formulas of the salts for metal ions with a +1 charge such as alkali metal ions (e.g., Li, Na, and K) are as follows. Squarate (M 2 C 4 O 4 ), Oxalate (M 2 C 2 O 4 ), Ketomalonate (M 2 C 3 O 5) and diketosuccinate (M 2 C 4 O 6 ). Here, M is a metal ion with a +1 charge. CO and CO that do not generate residues and can thus be removed after the cell formation cycle 2 All such salts are converted to gaseous products of.

[0028] According to a detailed embodiment, the sacrificial salt is selected from the group consisting of squarate and ketomalonate or combinations thereof. In a more detailed embodiment, the sacrificial salt has the formula M 2 C 4 O 4 where M is selected from Li, Na, and K. The chemical structures of Li 2 C 4 O 4 , Na 2 C 4 O 4 and K 2 C 4 O 4 and their decomposition reactions are shown below.

Chemical formula

[0029] The composite cathode can be formed of a mixture of a sacrificial salt and activated carbon in a suitable ratio. In an embodiment, the amount of the sacrificial salt in the composite electrode can range from about 10 wt% to about 60 wt% (e.g., about 10, about 20, about 30, about 40, about 50, or about 60 wt%). In a more detailed embodiment, the amount of the sacrificial salt in the composite electrode is about 40 wt%. In an embodiment, the amount of AC in the composite electrode can range from about 10 wt% to about 60 wt% (e.g., about 10, about 20, about 30, about 40, about 50, or about 60 wt%). In a more detailed embodiment, the amount of AC in the composite electrode is about 50 wt%. In an even more detailed embodiment, the composite cathode contains about 40 wt% of the sacrificial salt and about 50 wt% of AC.

[0030] The cathode and anode can be formed by casting (e.g., tape casting) a slurry mixture of the relevant components. The cathode slurry can include activated carbon and an optional binder, and the anode slurry can include hard carbon, an optional binder, and an optional conductive carbon source such as graphite or carbon black. Exemplary binders include, but are not limited to, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Specific examples of conductive carbon include, but are not limited to, super C45 and super C65.

[0031] For each of the cathode and anode, the amount of binder incorporated into the electrode can range from about 0 wt% to about 20 wt%, e.g., from about 5 wt% to about 10 wt%, of the total electrode composition. For the anode, the amount of conductive carbon incorporated into the electrode can range from about 0 wt% to about 10 wt% of the total anode composition, e.g., about 5 wt%.

[0032] In a detailed embodiment, the composite cathode includes about 40 wt% sacrificial salt, about 50 wt% AC, about 5 wt% C65 and about 5 wt% PVDF.

[0033] In some embodiments, the composite cathode containing activated carbon mixed with the sacrificial salt can be porous, while the hard carbon anode can be porous or non-porous, e.g., impermeable to a liquid containing a solvent used to form an electrolyte solution. The cathode and anode can each be attached to positive and negative current collectors, respectively. The current collector can include a metal foil such as copper foil or aluminum foil.

[0034] When assembled, the cathode, anode, separator and current collector can be collectively referred to as an electrode set. In some embodiments, the electrode set can consist essentially of the cathode, anode and separator, or can consist essentially of the cathode, anode, separator and their respective current collectors.

[0035] A liquid electrolyte solution can be incorporated between the cathode and the anode such that the electrolyte solution permeates through the separator. The electrolyte solution may include an electrolyte material (solute) dissolved in a suitable solvent. The electrolyte material can be any material that can function in an electrochemical device. In embodiments, the present invention relates to a lithium-ion capacitor in which the electrolyte material is a complex lithium salt such as a lithium salt, namely, LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiF 3 SO 3 , Li[(CF 3 SO 2 ) 2 N] or Li[(FSO 2 ) 2 N] and mixtures thereof. In embodiments, the present invention relates to a sodium-ion capacitor in which the electrolyte material is a complex sodium salt such as a sodium salt, namely, NaPF 6 , NaBF 4 , NaClO 4 , NaAsF 6 , NaF 3 SO 3 , Na[(CF 3 SO 2 ) 2 N] or Na[(FSO 2 ) 2 N] and mixtures thereof. In embodiments, the present invention relates to a potassium-ion capacitor in which the electrolyte material is a complex potassium salt such as a potassium salt, namely, KPF 6 , KBF 4 , KClO 4 , KAsF 6 , KF 3 SO 3 , K[(CF 3 SO 2 ) 2 N] or K[(FSO 2 ) 2Refers to a potassium ion capacitor which is a complex potassium salt such as [[ID=]], and mixtures thereof. Exemplary solvents for forming the electrolyte solution include dimethyl carbonate (DMC), methyl propionate (MP), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or mixtures thereof, and other organic solvents or mixtures of organic solvents such as other solvents suitable for use in electrolytes where the charge carriers are alkali metal ions such as lithium, sodium or potassium ions. In some embodiments, the solvent may be capable of dissolving the electrolyte material.

[0036] Complex salts such as complex lithium, sodium or potassium salts are any ionic compounds containing a metal such as lithium, sodium or potassium, and an additional metal, metalloid or non-metal atom which itself does not ionize and is soluble in an organic solvent. For example, LiPF 6 contains lithium and phosphorus as metal atoms, but phosphorus does not ionize by itself. Rather, phosphorus ionizes as PF 6 - ions. In a further example, LiBF 4 contains lithium metal and the metalloid boron. Lithium ionizes (Li + ), but boron does not ionize by itself and ionizes as BF 4 - ions. In yet a further example, LiClO 4 contains lithium metal as well as the non-metal atoms chlorine and oxygen. The non-metal atoms ionize as perchlorate ions (ClO 4 - ). The solvent can be any suitable solvent for use in an electrochemical energy storage device.

[0037] 6 In a detailed embodiment, the electrolyte solution is a solution of MPF

[0038] wherein M is preferably Li, Na or K in EC:PC.The electrolyte material and the sacrificial salt must be based on the same metal ion. In a detailed embodiment, the present invention refers to an alkali ion capacitor comprising an alkali metal sacrificial salt as a positive electrode additive and an electrolyte based on an alkali metal salt. In a more detailed embodiment, the present invention refers to a lithium ion capacitor comprising a lithium sacrificial salt as a positive electrode additive and an electrolyte based on a lithium salt. In a detailed embodiment, the present invention refers to a sodium ion capacitor comprising a sodium sacrificial salt as a positive electrode additive and an electrolyte based on a sodium salt. In a detailed embodiment, the present invention refers to a potassium ion capacitor comprising a potassium sacrificial salt as a positive electrode additive and an electrolyte based on a potassium salt.

[0039] A separator or ion-conductive membrane may be interposed between the anode and the cathode. The separator provides ion conductivity while ensuring effective separation between the opposing electrodes.

[0040] Basically, two types of separators can be used: a porous separator in which a solution of a solute in a suitable solvent fills the porosity of the separator, or generally a pure solid polymer electrolyte (i.e., an electrolyte dissolved in a high molecular weight polyether host such as PEO and PPO that functions as a solid solvent), or a gelled polymer electrolyte system in which a plasticizer or solvent capable of forming a stable gel within the polymer host matrix and the electrolyte is incorporated into the polymer matrix, i.e., a non-porous separator.

[0041] In a detailed embodiment, the separator is made of a fiberglass material.

[0042] One way to form a metal ion capacitor involves assembling an electrode set comprising a composite cathode, anode, and a separator disposed between the anode and the cathode, and then adding an electrolyte solution to the assembly.

[0043] According to a detailed embodiment, the positive electrode and the negative electrode are laminated or wound.

[0044] The metal ion capacitor of the present invention can find practical applications as a drive or auxiliary storage device for electric vehicles, hybrid electric vehicles, etc. Further, it is suitable as a storage device for various energy generation systems such as solar energy generation and wind power generation, and as a storage device for household electronic devices.

[0045] It is known to those skilled in the art that numerical values regarding measurements are subject to measurement errors that limit their accuracy. When terms such as "about" or "substantially" are applied to a specific value (e.g., "about 200 °C" or "substantially 200 °C") or a range (e.g., "about x to substantially y"), the value or range is interpreted as being as accurate as the method used to measure it. Unless specifically stated otherwise, the general rules in scientific and technical literature can preferably be applied such that the last digit of the numerical value indicates the accuracy of the measurement. Thus, unless other error limits are given, the maximum limit is preferably confirmed by applying the rounding rule to the last decimal place. For example, a value of 3.5 has an error limit of 3.45 to 3.54, and a range of 2% to 10% preferably includes a range of 1.5% to 10.4%. Such variations of the specified values are understood by those skilled in the art and are within the context of the present invention. Further, in order to provide a more concise description, some of the quantitative expressions given herein are not limited to the term "about". Whether or not the term "about" is explicitly used, all amounts given herein are meant to refer to the actual given value, which also includes equivalents and approximations due to experimental and / or measurement conditions for the given value, and refers to approximations to the given value reasonably inferred based on the ordinary skill in the art.

[0046] Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. This range format is used merely for convenience and brevity and should, therefore, be interpreted flexibly as including not only the numerical values explicitly recited as the limits of the range but also all the individual numerical values or sub-ranges subsumed within that range as if each were explicitly recited. For example, the numerical range “about 1% to about 5%” should be interpreted to include not only the explicitly recited values of about 1% to about 5% but also the individual values and sub-ranges within the indicated range. Thus, individual values such as 2, 3, and 4 and sub-ranges such as 1 - 3, 2 - 4, and 3 - 5 are included in this numerical range. This same principle applies to ranges that recite only a single numerical value.

[0047] It should be understood that the scope of the present disclosure includes all possible combinations of the embodiments disclosed herein.

Examples

[0048] The following examples are merely illustrative of specific embodiments of the present invention and should not be construed in any way as limiting it.

[0049] Example 1: Preparation of Sacrificial Salt Sacrificial salts, dilithium squarate (Li 2 C 4 O 4 ), disodium squarate (Na 2 C 4 O 4 ), and dipotassium squarate (K 2 C 4 O 4 ) are prepared from 4-dihydroxy-3-cyclobutene-1,2-dione and the respective metal carbonates (i.e., Li 2 CO 3 Na 2 CO 3 or K 2 CO 3) was synthesized using. A 1:1 mixture was taken, dissolved in deionized water, and then stirred overnight. The deionized water was removed by using a Buchi® Rotavapor and dried under vacuum at 50 °C for 12 hours before use.

[0050] Figure 1 shows the XRD pattern of the sacrificial salt.

[0051] Example 2: Preparation of Electrodes: HC and Composite AC / Sacrificial Salt Olive seeds were ground and filled in a tubular furnace for the pyrolysis process by heating them at a ramp rate of 5 °C / min to a preset temperature of 800 °C under an Ar flow of 100 ml / min and holding it for 2 hours to obtain further hard carbon (the active yield is ~25%). Then, before the HC was milled in a ball mill using balls made of jar and zirconia at an HC:ball mass ratio of 1:30 in a Pulverisette 5 (Fritsch International, Germany) to adjust the particle size and prepare HC for high-power applications, it was manually coarsely ground with a hard porcelain mortar / pestle. The milling was carried out for 90 minutes.

[0052] To prepare activated carbon (AC), the previously obtained hard carbon (HC) (without the grinding and ball milling steps) was physically mixed with potassium hydroxide at a mass ratio of 1 / 6. The material mixed with KOH was placed in an Inconel® boat and activated by heating it to a temperature of 700 °C under an Ar flow (100 ml / min) inside a horizontal stainless steel tube in a tubular furnace. The heating ramp rate was 5 °C / min and the holding time at the determined temperature was 2 hours. After activation, the microporous AC was washed with a dilute solution of hydrochloric acid and water until it reached a neutral pH and then dried at 120 °C under vacuum (the active yield is ~75%).

[0053] Along with the synthesized HC that functioned as the anode, AC was used as the sacrificial salt (Li 2 C 4O 4 、 Na 2 C 4 O 4 and K 2 C 4 O 4 ), respectively, and were mixed with conductive carbon (C65) and binder (PVDF).

[0054] Example 3: Lithium-Ion Capacitor A method for prelithiation of the negative electrode was studied in a lithium-ion capacitor comprising a hard carbon-based negative electrode fabricated in an airtight Swagelok cell, and a positive electrode based on activated carbon and Li 6 separated by fiberglass soaked in 1 M LiFP 2 C 4 O 4 in EC:DMC. Fig. 1a shows the XRD patterns of the synthesized lithium sacrificial salt (experiment, top) and the lithium sacrificial salt registered in the inorganic crystal structure database (ICDS, bottom).

[0055] Fig. 2 shows the electrochemical performance of the synthesized salts in a half-cell configuration to determine the decomposition potential and experimental capacity. Since the salts themselves are non-conductive organic compounds, the salts were mixed with conductive carbon (Super C65, Imerys Graphite & Carbon) to obtain a carbon coating on the salts in order to enable their decomposition. The potential window was set to 2 - 5 volts with respect to the corresponding M / M + . Fig. 2a shows the case for lithium squarate in a 1 M LiFP 6 EC:DMC electrolyte. The first CV cycle shows a broad peak of 3.8 - 4.5 V vs. Li+ / Li with a maximum value centered at 4.2 V. Furthermore, the second cycle still shows a broad but not very strong peak, indicating that some of the salt remains on the electrode after the first cycle. Nevertheless, the absence of peaks in subsequent cycles indicates that all lithium has been irreversibly extracted. Galvanostat (GA) charge / discharge measurements were performed at 2 - 4.2 V, and the potential window was determined from the CV. Specific capacity vs. Li +The Li / Li potential is shown in Fig. 2d. The first charge at C / 10 up to 4.2 V (where C corresponds to the theoretical capacity of Li 2 C 4 O 4 ) gives an irreversible specific capacity of 375 mAh / g and shows a large plateau at 3.8 - 4 V vs. Li + / Li. However, in the next cycle, the capacity is almost negligible corresponding to super C65.

[0056] Fig. 3 shows different sacrificial salts combined with AC for the development of the positive electrode, named "AC + salt" hereinafter. Fig. 3a shows Li 2 C 4 O 4 where the Li 2 C 4 O 4 is mixed with AC, conductive carbon (C65) and binder (PVDF) in weight ratios of 40 wt%, 50 wt%, 5 wt% and 5 wt% respectively. The CV shows a voltammogram recorded at 0.1 mV / s between 2 - 4.2 V vs. Li + / Li. The upper potential is limited by the instability of the electrolyte beyond that potential. In the first anodic sweep, the broad peak at 3.8 V - 4.2 V vs. Li + / Li represents the irreversible oxidation reaction of the salt. In subsequent cycles, a weak peak appears due to the salt remaining in the electrode. By the 10th cycle, only the typical rectangular voltammogram of AC can be recognized, confirming the overall decomposition of AC + salt while the contribution of AC remains unchanged. The GA charge / discharge was also followed. Fig. 3d shows the first charge step of the composite at C / 10 (where C is the theoretical specific capacity of Li 2 C 4 O 4 ) showing an irreversible specific capacity of 480 mAh / g with respect to the mass of the salt. This capacity higher than the theoretical capacity of the salt is due to the contribution of AC. Furthermore, the rate performance of the new positive electrode was followed between 2 - 4 V vs. Li + / Li and compared with a reference AC (without sacrificial salt, AC 参照 ) to see the possible influence of the residual products on the electrochemical performance.

[0057] Figure 4 shows the rate performance test conducted on the hard carbon material used during the assembly of the LIC. The GA charge / discharge measurements at different C-rates are shown, where C corresponds to the theoretical capacity of LiC 6 which is 372 mAh / g. In the first charging process at C / 10, the HC delivers 1063 mAh / g of which 461 mAh / g is reversible, showing a CE of 43.4%. The high irreversible capacity observed for the HC is attributed to its smaller particle size and the disordered nature that increases the electrode area. After 5 cycles, the capacity stabilizes at 394 mAh / g. Subsequent charge / discharge at 2C-rate delivers 260 mAh / g for the HC and maintains excellent specific capacity values at high power demand rates, i.e., 215 mAh / g at 10C, 120 mAh / g at 50C, and 70 mAh / g at 100C.

[0058] Figure 5 shows the rate performance test conducted on the hard carbon material used during the assembly of the LIC compared to a similar graphite electrode. The rate performance is very similar up to the 2C charge / discharge rate, but a difference starts to occur at 5C and it is already clear that at 10C, the HC has at least 2.5 times better performance than its graphite equivalent, and furthermore, this difference increases as the applied C-rate increases. Thus, the advantage of using HC over graphite for a powerful LIC is proven. On the other hand, the first CE for the HC is 42% while it is 72% for graphite.

[0059] In order to obtain the maximum capacity output of the electrodes and successfully overcome the first lithiation process, the active masses of the positive and negative electrodes need to be balanced such that the charges stored in both electrodes are equal (m+C+ΔV+=m-C-ΔV-). In Figure 6, the specific capacities of both electrodes are compared at various current densities. Thus, a mass ratio of 1:1 (HC:AC + salt) was selected for the development of the LIC.

[0060] Figure 7 shows the first galvanostatic lithiation of an HC-based LIC. First, the LIC (HC:AC + salt) was charged at C / 10 with respect to the mass of HC up to a fixed 4.2 V voltage at C / 10 with respect to the mass of HC. At the same time, Li + was extracted from the positive electrode and inserted into the microstructure of HC, enabling it to reach 330 mV vs. Li + / Li. The subsequent cycles and system as well as electrode performance were evaluated in Figure 8, where the various charge / discharge profiles of AC (red dashed line), HC (green dash-dotted line), and full LIC (black solid line) at various current densities are shown, ranging from the discharge time available by the battery (30 minutes) to the discharge time limited for the EDLC (15 seconds). At low current density, within a discharge time of ~30 minutes, AC shows a symmetric shape indicating its capacitive storage mechanism. AC swings in two swings at 2.8 - 4.3 V vs. Li+ / Li, while HC shows a loose profile and swings at 860 - 380 mV vs. Li+ / Li. When the current density applied at 0.5 A / g within a discharge time of ~2.5 minutes is further increased, both systems maintain similar behavior, but the potential window of the negative electrode becomes slightly wider. Still, HC still functions at a safe potential away from the plating potential. As the applied current density is increased towards the discharge time typically limited for the EDLC, HC shows remarkable behavior within a discharge time of only 15 seconds.

[0061] The energy and power density values are referenced to the sum of the active masses (AM) (mg of HC and mg of AC) of both electrodes and are reported in the Ragone plot of Figure 9. High energy density values are achieved at various power densities for both devices. Still, the ultra-fast response achieved by the HC-based LIC overcomes the energy characteristics of the graphite-based LIC from the perspective of high-power applications. A 2 - 3-fold increase is observed in the energy density along with various power density requirements compared to a conventional EDLC based on symmetric olive-derived AC.

[0062] Example 4: Sodium-Ion Capacitor A method for pre-sodiation of the negative electrode was studied in a sodium-ion capacitor comprising a hard carbon-based negative electrode fabricated in an airtight Swagelok cell, as well as a positive electrode based on activated carbon and Na 6 C separated by fiberglass immersed in EC:PC, and Na 2 C 4 O 4 XRD patterns of the synthesized sodium sacrificial salt (experiment, top) and the sodium sacrificial salt registered in the inorganic crystal structure database (ICDS, bottom) are shown in Fig. 1b.

[0063] As described above, Fig. 2 shows the electrochemical performance of the synthesized salts in a half-cell configuration to determine the decomposition potential and experimental capacity. Fig. 2b shows the case of sodium squarate in 1M NaPF 6 EC:PC. The first cycle shows a broad peak at 3.5 - 4.15 V vs. Na 2 C 4 O 4 / Na where the decomposition of Na + C + O 2 C 4 O 4 occurs. The second cycle shows a broad but not very strong peak due to the salt remaining on the electrode after the first cycle. Nevertheless, the absence of peaks in subsequent cycles indicates that all the salts have decomposed irreversibly. Fig. 2e shows the GA charge / discharge measurements performed within the 2 - 4.2 V vs. Na

[0064] / Na potential window. (C is the theoretical capacity of Na 2 C 4 O 4 corresponding to 339.268 mAh / g. The first charge at C / 10 up to 4.2 V shows a broad profile at 3.7 - 4.2 V vs. Na+ / Na where an irreversible specific capacity of 275 mAh / g is obtained. In the next cycle, the capacity is almost zero corresponding to super C65. 2 C 4 O 4is mixed with AC, conductive carbon (C65) and binder (PVDF) in weight ratios of 40 wt%, 50 wt%, 5 wt% and 5 wt% respectively. CV shows a voltammogram recorded at 2 - 4.2V vs. Li + / Li, 0.1 mV / s. The upper potential is limited by the instability of the electrolyte beyond that potential. In the first anodic sweep, a broad peak at 3.6V - 4V vs. Li + / Li represents the irreversible oxidation reaction of the salt. In subsequent cycles, a weak peak appears due to the salt remaining on the electrode. By the 10th cycle, only the typical rectangular voltammogram of AC can be recognized, and the overall decomposition of AC + salt is confirmed while the contribution of AC remains invariant. GA charge / discharge was also tracked. Figure 3e shows the first charging process of the composite at C / 10 (C is the theoretical specific capacity of Na 2 C 4 O 4 ), showing an irreversible specific capacity of 350 mAh / g with respect to the mass of the salt. This capacity, higher than that measured for the reference salt, is due to the contribution of AC.

[0065] To obtain the maximum capacity output of the electrode and successfully overcome the first sodiation process, the charges stored in both electrodes must be equal (m + C + ΔV + = m - C - ΔV - ), so the active masses of the positive and negative electrodes need to be balanced. In Figure 10, the rate performance of the HC and AC + Na 2 C 4 O 4 composites is summarized to set the correct mass ratio of the device. In this case, a 1:1 mass ratio was selected to avoid further sodium plating at high current densities due to the loose capacity values of HC along various current densities.

[0066] Figure 11 shows the first charging process up to 4.2 V at C / 10 with respect to the mass of HC. In this process, while the whole device is being charged, the sodium-based sacrificial salt at the positive electrode is oxidized at a potential of 3.5 - 4 V vs. Na + / Na, and further, the extracted Na + is inserted into the microstructure of HC, and a cut-off potential of 180 mV is achieved.

[0067] After the pre-sodiation process was completed, the GA charge / discharge measurements were followed for NIC at a cell voltage of 2 - 4 V at various current densities. Figure 12 shows the various charge / discharge profiles of AC (red dashed line), HC (green dash-dotted line) and full NIC (black solid line) at various current densities. In all of them, the AC potential window swings between 3 - 4 V vs. Na + / Na, while the HC potential window swings between 1 V to ~300 mV vs. Na+ / Na, avoiding any sodium plating on the surface of the negative electrode. The energy and power density values, referenced to the total active mass (AM) (mg of HC and mg of AC) of both electrodes of the pre-sodiated NIC, are reported in a Ragone plot in Figure 13. At low power density, within a discharge time of ~30 minutes, the developed pre-sodiated NIC can deliver as much energy density as its LIC counterpart, which is about 72 Wh / kg AM . Increasing the applied current density towards a discharge time of ~10 minutes, the energy density is still maintained at 58 Wh / kg AM . Still, due to the hindrance of Na+ diffusion at high rates, the NIC delivers a lower specific energy value than the developed LIC. However, it can still provide an energy density value higher than its EDLC counterpart up to a power density of 2000 Wh / kg AM within a discharge time of ~1 minute without any sodium plating.

[0068] Example 5: Potassium-Ion Capacitor Figure 1c shows the XRD pattern of the potassium sacrificial salt.

[0069] As described above, FIG. 2 shows the electrochemical performance of the synthesized salt in a half-cell configuration to determine the decomposition potential and the experimental capacity. FIG. 2c shows the case of potassium squarate in 1M KPF 6 in EC:DMC. The first cycle shows a broad peak of 3.5 - 4.5V vs. K 2 C 4 O 4 / K where the decomposition of K + / K occurs. Further, the increase in current is due to electrolyte decomposition. In subsequent cycles, the peak at 3.5 - 4.5V disappears, but the peak above 4.5V confirms electrolyte decomposition. FIG. 2f shows the GA charge / discharge measurements performed within the 2 - 4.5V vs. K + / K potential window. (C corresponds to the theoretical capacity of K 2 C 4 O 4 which is 282 mAh / g. The first charge at C / 10 up to 4.5V shows a broad profile of 3.6 - 4.5V vs. K + / K where an irreversible specific capacity of 225 mAh / g is obtained. In the next cycle, the capacity is almost zero corresponding only to super C65.

[0070] FIG. 3c shows K 2 C 4 O 4 and the K 2 C 4 O 4 is mixed with AC, conductive carbon (C65) and binder (PVDF) in weight ratios of 40 wt%, 50 wt%, 5 wt% and 5 wt% respectively. The CV shows a voltammogram recorded at 2 - 4.2V vs. Li + / Li, 0.1 mV / s. The upper potential is limited by the instability of the electrolyte beyond that potential. In the first anodic sweep, 3.6V - 4.2V vs. Li +The broad peak of / Li represents the irreversible oxidation reaction of the salt. In subsequent cycles, a weak peak appears due to the salt remaining on the electrode. By the 10th cycle, only the typical rectangular voltammogram of AC can be recognized, and the overall decomposition of AC + salt is confirmed while the contribution of AC remains unchanged. GA charge / discharge was also tracked. Figure 3f shows the first charging process of the composite at C / 10 (where C is the theoretical specific capacity of K 2 C 4 O 4 ), showing an irreversible specific capacity of 250 mAh / g with respect to the mass of the salt. This capacity, which is higher than that measured for the reference salt, is due to the contribution of AC.

[0071] To obtain the maximum capacity output of the electrode and successfully overcome the first pre-potassiation process, the charges stored in both electrodes must be equal (m + C + ΔV + =m - C - ΔV - ), so the active masses of the positive and negative electrodes need to be balanced. In Figure 14, the rate performance of the HC and AC + K 2 C 4 O 4 composites is summarized to set the correct mass ratio of the device. In this case, a 1:1 mass ratio was selected to avoid further potassium plating at high current densities due to the loose capacity values of HC along various current densities.

[0072] Figure 15 shows the first charging process of the HC to a fixed 4.2 V at C / 10 with respect to the mass of the HC. In this process, while the entire device is being charged, the potassium-based sacrificial salt in the positive electrode is oxidized at a potential of 3.5 - 4.2 V vs. K + / K, and further, the extracted K + is inserted into the microstructure of the HC, and a cut-off potential of 600 mV is achieved.

Claims

1. a negative electrode containing hard carbon, a positive electrode comprising activated carbon and a sacrificial salt, the salt being mixed with conductive carbon and having a carbon coating on the salt; and - a separator positioned between said two electrodes; A metal ion capacitor wherein said sacrificial salt is a squarate salt of formula M 2 C 4 O 4 , where M is selected from Li, Na and K.

2. The metal ion capacitor of claim 1 , wherein the metal ion capacitor is an alkali metal ion capacitor.

3. The metal ion capacitor of claim 1 , wherein the metal ion capacitor is a lithium, sodium or potassium capacitor.

4. 4. The metal ion capacitor of claim 1, wherein the hard carbon of the negative electrode has an average particle size in the range of about 0.1 to about 5 microns.

5. The metal ion capacitor of any one of claims 1 to 4, wherein the positive electrode comprises about 10-60% by weight of a sacrificial salt.

6. 6. A method for manufacturing the metal ion capacitor of any one of claims 1 to 5, the method comprising producing the activated carbon of the negative hard carbon electrode and / or the positive electrode from biomass waste.

7. 7. The method for manufacturing the metal ion capacitor of claim 6, wherein the method comprises the preparation of the activated carbon of the negative hard carbon electrode and / or the positive electrode from olive pits.

8. A method for pre-doping a negative electrode of a metal ion capacitor and for supplementing the need for metal ions to form a solid electrolyte interphase (SEI) on the negative electrode, the method comprising using a sacrificial salt as a source of metal ions, the sacrificial salt being combined with activated carbon at a positive electrode, the sacrificial salt being represented by the formula M ２ C ４ O ４ wherein M is selected from Li, Na and K, said sacrificial salt is mixed with conductive carbon to provide a carbon coating on said salt, and said negative electrode comprises hard carbon.

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