Patent Application
20240021875
Not applicable.
This disclosure relates to electrolytes that can facilitate transport of ions with wide applications in electrochemical devices, such as batteries.
To reduce carbon emissions and realize carbon neutrality, it is essential to develop sustainable rechargeable batteries for the storage of renewable energy [Ref.1,2]. Aqueous rechargeable batteries, such as Zn-metal batteries, which use a Zn-metal anode and water-based electrolytes, are attractive candidates to fulfill these energy storage demands due to their inherent safety, fast charging/discharging capability, environmental friendliness, wide material availability, and low cost [Ref. 3,4]. Conventional zinc metal batteries comprise an anode including zinc metal, a cathode including a zinc host material, a separator material that keeps the anode and the cathode from touching but allows Zn2+ ions through, and a liquid electrolyte (e.g., an aqueous or non-aqueous electrolyte including zinc salts). During a typical discharge process, zinc ions from the anode are extracted into the electrolyte, and zinc ions in the electrolyte are intercalated into the cathode material. This movement of the ions from anode to cathode is accompanied by the release of electrons which flow in the external circuit. The reverse process occurs during the charging process where zinc ions move from the cathode to the anode through the electrolyte.
However, rechargeable Zn-metal batteries have yet to be commercialized, largely because of problems associated with the Zn-metal anode, including undesired Zn dendrite formation, corrosion, and hydrogen generation during the Zn plating/stripping process [Ref. 5,6], all of which can cause low cycling reversibility and ultimately battery failure. These issues mainly stem from the unregulated Zn-deposition morphology at high current densities as well as the high free-water content in conventional aqueous electrolytes, which reacts with the Zn-metal during electrochemical cycling [Ref. 7-10]. The aqueous electrolyte induces surface passivated reactions on the Zn surface, which leads to inhomogeneous Zn deposition that causes possible dendrite penetration through the separator and low cycling reversibility [Ref. 11-13]. To address these challenges, extensive efforts have been devoted to modifying the electrolyte, including the use of high-salt-concentration “water-in-salt” electrolytes [Ref. 14-16], various additives to aqueous electrolytes (such as ethylene glycol as a water blocker) [Ref. 17,18], or organic electrolytes [Ref. 19,20]. However, these strategies sacrifice the intrinsic high conductivity of aqueous electrolytes and/or compromise the safety of the Zn-metal battery [Ref. 21]. There are reports of hydrogel electrolytes that show promise at inhibiting Zn dendrites, as the nanochannels and polar groups of the hydrogel can control the free-water content and enhance the uniformity of the current distribution [Ref. 9,22-24]. However, current hydrogel electrolytes do not meet the high mechanical strength, high rate capability, and long-term cycling stability needed for high-performance Zn-metal batteries [Ref. 1, 25].
What is needed therefore are improved electrolytes that meet the high mechanical strength, high rate capability, and long-term cycling stability needed for high-performance Zn-metal batteries.
The present disclosure addresses the foregoing needs by providing a chitosan material that can act as an electrolyte in an electrochemical device.
In one aspect, the disclosure provides an electrolyte comprising a plurality of chitosan molecular chains crosslinked with zinc cations. In one embodiment, the electrolyte has a zinc ion conductivity of greater than 30 mS cm−1 at room temperature. In one embodiment, the electrolyte has a zinc ion conductivity is greater than 70 mS cm−1 at room temperature. In one embodiment, the electrolyte has a water content of 20 wt. % to 75 wt. % based on a total weight of the electrolyte. In one embodiment, the electrolyte has pores below micrometer scale. In one embodiment, the electrolyte has nanopores. In one embodiment, the electrolyte has no pores above micrometer scale. In one embodiment, the electrolyte has a BET surface area of at least 16 m2 g−1. In one embodiment, the electrolyte has a tensile strength of at least 2 MPa. In one embodiment, the electrolyte has a tensile strength of at least 5 MPa. In one embodiment, the zinc cations are coordinated with amino groups and hydroxyl groups of the chitosan molecular chains. In one embodiment, the electrolyte has a thickness in a range of 1 to 1000 micrometers. In one embodiment, the plurality of chitosan molecular chains are crosslinked by contacting the plurality of chitosan molecular chains with the zinc cations in an alkaline environment. In one embodiment, the plurality of chitosan molecular chains are crosslinked by contacting the plurality of chitosan molecular chains with the zinc cations in a hydroxide solution.
In another aspect, the disclosure provides an electrochemical device comprising: an anode; a cathode; and an electrolyte positioned between the anode and the cathode, wherein the electrolyte comprises a plurality of chitosan molecular chains crosslinked with zinc cations. In one embodiment, the device is a zinc ion battery, and the cathode comprises a zinc host material selected from the group consisting of (i) metal oxides, metal sulfides, metal phosphates, and metal selenides wherein the metal is one or more of manganese, vanadium, zinc, lithium, cobalt, iron, molybdenum, titanium, niobium, bismuth and tungsten, (ii) poly(benzoquinonyl sulfide), (iii) lead titanate, (iv) Prussian blue compounds, (v) electrically conductive polymers, and (vi) mixtures thereof. In one embodiment, the cathode comprises poly(benzoquinonyl sulfide). In one embodiment, the anode comprises a material selected from metallic zinc and zinc alloys. In one embodiment, the zinc ion battery includes a zinc-deposition morphology of zinc platelets on the anode. In one embodiment, the zinc ion battery includes a zinc-deposition morphology of hexagonal zinc platelets with an orientation parallel to a surface of the anode. In one embodiment, the platelets have a size greater than 500 nanometers. In one embodiment, the zinc ion battery has an areal capacity greater than 2 mAh cm−2 at a current density of 5 mA cm−2. In one embodiment, the zinc ion battery has a Coulombic efficiency greater than 98% over 400 cycles at a C-rate of 2C. In one embodiment, the zinc ion battery has a capacity retention of greater than 60% over 400 cycles at a C-rate of 2C. In one embodiment, the device is a zinc air battery, and the cathode comprises porous carbon.
In still another aspect, the disclosure provides an electrode comprising: a zinc host material; and an electrolyte comprising a plurality of chitosan molecular chains crosslinked with zinc cations. In one embodiment, the electrode includes 2 wt. % to 20 wt. % of the electrolyte based on a total weight of the electrode. In one embodiment, the zinc host material is selected from the group consisting of (i) metal oxides, metal sulfides, metal phosphates, and metal selenides wherein the metal is one or more of manganese, vanadium, zinc, lithium, cobalt, iron, molybdenum, titanium, niobium, bismuth and tungsten, (ii) poly(benzoquinonyl sulfide), (iii) lead titanate, (iv) Prussian blue compounds, (v) electrically conductive polymers, and (vi) mixtures thereof. In one embodiment, the electrolyte has a zinc ion conductivity of greater than 70 mS cm−1 at room temperature. In one embodiment, the electrolyte has nanopores. In one embodiment, the electrolyte has a BET surface area of at least 16 m2 g−1. In one embodiment, the electrolyte has a tensile strength of at least 5 MPa. In one embodiment, the zinc cations are coordinated with amino groups and hydroxyl groups of the chitosan molecular chains.
In yet another aspect, the disclosure provides a method for forming an electrolyte. The method can comprise: (a) casting a flowable composition including chitosan on a support to form a chitosan membrane on the support; (b) contacting the chitosan membrane with a solution including zinc cations to form a chitosan-Zn membrane; and (c) separating the chitosan-Zn membrane from the support to form an electrolyte comprising a plurality of chitosan molecular chains crosslinked with zinc cations. In one embodiment of the method, step (b) further comprises applying a pressure to the chitosan-Zn membrane after contacting the chitosan membrane with the solution, the pressure being above atmospheric pressure. In one embodiment of the method, step (b) comprises immersing the chitosan membrane on the support in a bath containing the solution, wherein the solution is an alkaline solution. In one embodiment of the method, the solution is a hydroxide solution. In one embodiment of the method, the solution is a Zn2+-saturated hydroxide solution. In one embodiment of the method, the solution is a Zn2+-saturated NaOH solution. In one embodiment of the method, step (a) comprises transporting the support from a roll of the support to a zone where the flowable composition including chitosan is cast on the support. In one embodiment of the method, step (c) comprises collecting the electrolyte on a roll after separating the electrolyte from the support. In one embodiment of the method, step (b) comprises applying a pressure of 1 MPa or greater. In one embodiment of the method, step (b) comprises applying a pressure in a range of 1 MPa to 10 MPa. In one embodiment of the method, step (b) comprises applying the pressure such that the electrolyte has pores below micrometer scale. In one embodiment of the method, step (b) comprises applying the pressure such that the electrolyte has no pores above micrometer scale. In one embodiment of the method, step (b) comprises applying the pressure such that the electrolyte has a BET surface area of at least 16 m2 g−1. In one embodiment of the method, step (b) comprises applying the pressure such that the electrolyte has a tensile strength of at least 2 MPa. In one embodiment of the method, the flowable composition includes 1 wt. % to 10 wt. % chitosan based on a total weight of the flowable composition. In one embodiment of the method, step (b) further comprises washing the chitosan-Zn membrane with water.
A Zn-metal battery is a promising clean energy-storage device, but its application is hindered by uncontrolled Zn deposition in the Zn-metal anode. We have found that a biomaterial-derived chitosan-Zn electrolyte enables favorable Zn-platelet deposition due to its high mechanical strength, high Zn2+ conductivity, and water bonding capability. The chitosan-Zn electrolyte not only enables high-rate and long-life performance but is also biodegradable, appealing for clean and efficient energy storage.
These and other features, aspects, and advantages of examples provided in the present disclosure will become better understood upon consideration of the following detailed description, drawings, and appended claims.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
Before any embodiments of this disclosure are explained in detail, it is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The presented examples are capable of other embodiments and of being practiced or of being carried out in various ways.
It is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. As used herein, the term “C-rate” can be understood as follows. Charge and discharge rates of a battery are governed by C-rates. The capacity of a battery is commonly rated at 1C, meaning that a fully charged battery rated at 1 Ah should provide 1 amp (A) for one hour. The same battery discharging at 0.5C should provide 0.5 A for two hours, and at 2C, it delivers 2 A for 30 minutes. As illustrative examples, a C-rate of 1C is also known as a one-hour charge or discharge; a C-rate of 4C is a ¼-hour charge or discharge; a C-rate of 2C is a ½-hour charge or discharge; a C-rate of 0.5C or C/2 is a 2-hour charge or discharge; a C-rate of 0.2C or C/5 is a 5-hour charge or discharge, and a C-rate of 0.1C or C/10 is a 10-hour charge or discharge.
The following discussion is presented to enable a person skilled in the art to make and use embodiments of the disclosure. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the disclosure. Thus, embodiments of the disclosure are not intended to be limited to embodiments shown and described but are to be accorded the widest scope consistent with the principles and features disclosed herein. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the disclosure.
The electrolytes of the present disclosure can be used in a battery such as the non-limiting example zinc ion battery 110 as shown in
The first current collector 112 and the second current collector 122 can comprise a conductive metal or any suitable conductive material. In some embodiments, the first current collector 112 and the second current collector 122 comprise zinc, aluminum, nickel, copper, combinations and alloys thereof. It is to be appreciated that the thicknesses depicted in
A suitable active material for the cathode 114 of the zinc ion battery 110 is a zinc host material capable of storing and subsequently releasing zinc ions. The cathode 114 can comprise a zinc host material selected from the group consisting of (i) metal oxides, metal sulfides, metal phosphates, and metal selenides wherein the metal is one or more of manganese, vanadium, zinc, lithium, cobalt, iron, molybdenum, titanium, niobium, bismuth and tungsten, (ii) poly(benzoquinonyl sulfide), (iii) lead titanate, (iv) Prussian blue compounds, (v) electrically conductive polymers (such as polyaniline, polyacetylene, polypyrene, and polyorganosulfides), and (vi) mixtures thereof. The cathode 114 can optionally further comprise an electrolyte according to any embodiments of the present disclosure wherein the electrolyte is present in the cathode at a weight percentage in a range of 2 wt. % to 20 wt. % based on a total weight of the cathode. In other embodiments, the cathode 114 of the zinc ion battery 110 can comprise porous carbon (for a zinc air battery). The cathode 114 can optionally further comprise a conductive filler such as Ketjen black, acetylene black, nanoporous carbon, graphite, furnace black, channel black, and mixtures thereof. The cathode 114 can optionally further comprise a binder such as a polyimide, an acrylate, ethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, a polyolefin, ethylene-propylene-diene terpolymer, an alkyl vinyl ether, a fluororubber, and mixtures thereof.
In some embodiments, a suitable active material for the anode 118 of the zinc ion battery 110 comprises a material selected from metallic zinc and zinc alloys. In one embodiment, the anode 118 of the zinc ion battery 110 consists essentially of metallic zinc or a zinc alloy. Non-limiting examples of zinc alloys that may be used in the anode include alloys of zinc with one or more of lead, vanadium, chromium, manganese, iron, cobalt, nickel, cadmium, tungsten, bismuth, tin, indium, antimony, copper, and titanium.
The electrolyte for the battery 110 may be an electrolyte according to any embodiments of the present disclosure. An electrolyte of the present disclosure comprises a plurality of chitosan molecular chains crosslinked with zinc cations. Chitosan is a natural material that includes a plurality of molecular chains of polysaccharides, more specifically, the molecular chains are a random distributed units of β-(1→4)-linked D-glucosamine (deacetylated unit) and units of N-acetyl-D-glucosamine. According to an aspect of the disclosure herein, the plurality of chitosan molecular chains can be crosslinked with zinc cations, such as Zn2+, to form an electrolyte. The zinc cations coordinate between the chains along at least a portion of the chitosan molecular chains. The zinc cations can be coordinated with amino groups and/or hydroxyl groups of the chitosan molecular chains. The plurality of chitosan molecular chains can be crosslinked by contacting the plurality of chitosan molecular chains with the zinc cations in an alkaline environment. The plurality of chitosan molecular chains can be crosslinked by contacting the plurality of chitosan molecular chains with the zinc cations in a hydroxide solution.
In certain embodiments, the electrolyte has a zinc ion conductivity of greater than 30 mS cm−1 at room temperature, or a zinc ion conductivity of greater than 40 mS cm−1 at room temperature, or a zinc ion conductivity of greater than 50 mS cm−1 at room temperature, or a zinc ion conductivity of greater than 60 mS cm−1 at room temperature, or a zinc ion conductivity of greater than 70 mS cm−1 at room temperature.
In certain embodiments, the electrolyte has a water content of 20 wt. % to 75 wt. % based on a total weight of the electrolyte, or a water content of 30 wt. % to 70 wt. % based on a total weight of the electrolyte, or a water content of 40 wt. % to 70 wt. % based on a total weight of the electrolyte, or a water content of 50 wt. % to 70 wt. % based on a total weight of the electrolyte.
In certain embodiments, the electrolyte has pores below micrometer scale. In certain embodiments, the electrolyte has nanopores. In certain embodiments, the electrolyte has no pores above micrometer scale. In certain embodiments, the electrolyte has a BET surface area of at least 16 m2 g−1.
In certain embodiments, the electrolyte has a tensile strength of at least 2 MPa, or a tensile strength of at least 3 MPa, or a tensile strength of at least 4 MPa, or a tensile strength of at least 5 MPa, or a tensile strength of at least 6 MPa, or a tensile strength of at least 7 MPa.
In certain embodiments, the electrolyte has a thickness in a range of 1 to 1000 micrometers, or in a range of 1 to 500 micrometers, or in a range of 1 to 100 micrometers.
An electrolyte of the present disclosure can be incorporated into an electrochemical device including any of the cathode and anode materials described above. In certain embodiments, the device is a zinc ion battery, and the cathode comprises a zinc host material selected from the group consisting of (i) metal oxides, metal sulfides, metal phosphates, and metal selenides wherein the metal is one or more of manganese, vanadium, zinc, lithium, cobalt, iron, molybdenum, titanium, niobium, bismuth and tungsten, (ii) poly(benzoquinonyl sulfide), (iii) lead titanate, (iv) Prussian blue compounds, (v) electrically conductive polymers, and (vi) mixtures thereof. In one embodiment, the cathode comprises poly(benzoquinonyl sulfide), and the anode comprises a material selected from metallic zinc and zinc alloys. In one embodiment, the zinc ion battery can include a zinc-deposition morphology of zinc platelets on the anode. In one embodiment, the zinc ion battery includes a zinc-deposition morphology of hexagonal zinc platelets with an orientation parallel to a surface of the anode. In one embodiment, the platelets have a size greater than 500 nanometers. In one embodiment, the platelets have a size greater than 1 micrometer.
In one embodiment, the zinc ion battery has an areal capacity greater than 2 mAh cm−2 at a current density of 5 mA cm−2. In one embodiment, the zinc ion battery has a Coulombic efficiency greater than 98% over 400 cycles at a C-rate of 2C. In one embodiment, the zinc ion battery has a Coulombic efficiency greater than 99% over 400 cycles at a C-rate of 2C. In one embodiment, the zinc ion battery has a capacity retention of greater than 60% over 400 cycles at a C-rate of 2C. In one embodiment, the zinc ion battery has a capacity retention of greater than 70% over 400 cycles at a C-rate of 2C.
In one embodiment, the device is a zinc air battery, and the cathode comprises porous carbon.
An electrolyte of the present disclosure can be incorporated into a composite electrode comprising a zinc host material. The electrode can be a cathode or an anode. In one embodiment, the electrode includes 2 wt. % to 20 wt. % of the electrolyte based on a total weight of the electrode. The zinc host material can be selected from the group consisting of (i) metal oxides, metal sulfides, metal phosphates, and metal selenides wherein the metal is one or more of manganese, vanadium, zinc, lithium, cobalt, iron, molybdenum, titanium, niobium, bismuth and tungsten, (ii) poly(benzoquinonyl sulfide), (iii) lead titanate, (iv) Prussian blue compounds, (v) electrically conductive polymers, and (vi) mixtures thereof. In one embodiment of the electrode, the electrolyte has a zinc ion conductivity of greater than 70 mS cm−1 at room temperature. In one embodiment of the electrode, the electrolyte has nanopores. In one embodiment of the electrode, the electrolyte has a BET surface area of at least 16 m2 g−1. In one embodiment of the electrode, the electrolyte has a tensile strength of at least 5 MPa. In one embodiment of the electrode, the zinc cations are coordinated with amino groups and hydroxyl groups of the chitosan molecular chains. In one embodiment of the electrode, the plurality of chitosan molecular chains are crosslinked by contacting the plurality of chitosan molecular chains with the zinc cations in a hydroxide solution.
The electrolyte of the present disclosure can be formed according to the following non-limiting example methods. The method can comprise: (a) casting a flowable composition including chitosan on a support to form a chitosan membrane on the support; (b) contacting the chitosan membrane with a solution including zinc cations to form a chitosan-Zn membrane; and (c) separating the chitosan-Zn membrane from the support to form an electrolyte comprising a plurality of chitosan molecular chains crosslinked with zinc cations. Step (b) can further comprise applying a pressure to the chitosan-Zn membrane after contacting the chitosan membrane with the solution, wherein the pressure is above atmospheric pressure. The flowable composition can include 1 wt. % to 10 wt. % chitosan based on a total weight of the flowable composition. In one embodiment of the method, step (b) comprises immersing the chitosan membrane on the support in a bath containing the solution, wherein the solution is an alkaline solution. In one embodiment of the method, the solution is a hydroxide solution. In one embodiment of the method, the solution is a Zn2+-saturated NaOH solution. In one embodiment of the method, step (b) further comprises washing the chitosan-Zn membrane with water.
In one embodiment of the method, step (a) comprises transporting the support from a roll of the support to a zone where the flowable composition including chitosan is cast on the support. In one embodiment of the method, step (c) comprises collecting the electrolyte on a roll after separating the electrolyte from the support. In one embodiment of the method, step (b) comprises applying a pressure of 1 MPa or greater, or applying a pressure of in a range of 1 MPa to 10 MPa.
In one embodiment of the method, step (b) comprises applying the pressure such that the electrolyte has pores below micrometer scale. In one embodiment of the method, step (b) comprises applying the pressure such that the electrolyte has no pores above micrometer scale. In one embodiment of the method, step (c) comprises applying the pressure such that the electrolyte has a BET surface area of at least 16 m2 g−1. In one embodiment of the method, step (b) comprises applying the pressure such that the electrolyte has a tensile strength of at least 2 MPa, or a tensile strength of at least 3 MPa, or a tensile strength of at least 4 MPa, or a tensile strength of at least 5 MPa, or a tensile strength of at least 6 MPa, or a tensile strength of at least 7 MPa.
The following Example has been presented in order to further illustrate the aspects of the present disclosure and is not intended to limit the present disclosure in any way. The statements provided in the Example are presented without being bound by theory.
Rechargeable aqueous Zn-metal battery is promising for grid energy storage needs, but its application is limited by issues such as Zn dendrite formation. In this Example, we demonstrate a Zn-coordinated chitosan (chitosan-Zn) electrolyte for high-performance Zn-metal batteries. The chitosan-Zn electrolyte exhibits high mechanical strength, Zn2+ conductivity, and water bonding capability, which enable a desirable Zn-deposition morphology of parallel hexagonal Zn platelets. Using the chitosan-Zn electrolyte, the Zn anode shows exceptional cycling stability and rate performance, with a high Coulombic efficiency of 99.7% and >1,000 cycles at 50 mA cm−2. The full batteries show excellent high-rate performance (up to 20C, 40 mA cm−2) and long-term cycling stability (>400 cycles at 2C). Furthermore, the chitosan-Zn electrolyte is non-flammable and biodegradable, making the Zn-metal battery appealing in terms of safety and sustainability, demonstrating the promise of sustainable biomaterials for green and efficient energy-storage systems.
To reduce carbon emissions and realize carbon neutrality, it is essential to develop sustainable rechargeable batteries for the storage of renewable energy [Ref.1,2]. Aqueous rechargeable batteries, such as Zn-metal batteries, which use a Zn-metal anode and water-based electrolytes, are attractive candidates to fulfill these energy storage demands due to their inherent safety, fast charging/discharging capability, environmental friendliness, wide material availability, and low cost [Ref. 3,4]. However, rechargeable Zn-metal batteries have yet to be commercialized, largely because of problems associated with the Zn-metal anode, including undesired Zn dendrite formation, corrosion, and hydrogen generation during the Zn plating/stripping process [Ref. 5,6], all of which can cause low cycling reversibility and ultimately battery failure.
These issues mainly stem from the unregulated Zn-deposition morphology at high current densities as well as the high free-water content in conventional aqueous electrolytes, which reacts with the Zn-metal during electrochemical cycling [Ref. 7-10]. The aqueous electrolyte induces surface passivated reactions on Zn surface, which leads to inhomogeneous Zn deposition that causes possible dendrite penetration through the separator and low cycling reversibility [Ref. 11-13]. To address these challenges, extensive efforts have been devoted to modifying the electrolyte, including the use of high-salt-concentration “water-in-salt” electrolytes [Ref. 14-16], various additives to aqueous electrolytes (such as ethylene glycol as a water blocker) [Ref. 17,18], or organic electrolytes [Ref. 19,20]. However, these strategies sacrifice the intrinsic high conductivity of aqueous electrolytes and/or compromise the safety of the Zn-metal battery [Ref. 21]. There are reports of hydrogel electrolytes that show promise at inhibiting Zn dendrites, as the nanochannels and polar groups of the hydrogel can control the free-water content and enhance the uniformity of the current distribution [Ref. 9, 22-24]. However, current hydrogel electrolytes do not meet the high mechanical strength, high rate capability, and long-term cycling stability needed for high-performance Zn-metal batteries [Ref. 1, 25].
In this Example, we demonstrate a biopolymeric chitosan-Zn gel electrolyte for high-rate and long-life Zn-metal batteries that features a strong combination of high ionic conductivity, mechanical strength, and sustainability while also enabling a desirable deposition morphology of parallel hexagonal Zn platelets (rather than Zn dendrites) on the anode surface. Chitosan is an eco-friendly and biodegradable biopolymer derived from naturally abundant chitin, which is widely available in crustacean shells [Ref. 26]. The chitosan molecules contain rich hydroxyl and amine groups that can form hydrogen bonds with water to reduce the content of free water in the chitosan-Zn gel electrolyte. We fabricate this gel electrolyte by first coordinating the chitosan biopolymer with Zn2+ in a Zn2+-saturated NaOH solution and then squeezing out excess water by compressing the material, forming a densified chitosan-Zn membrane (
We prepared the chitosan-Zn membrane using a two-step process (
We performed X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy to investigate the chemical valences and bonding states in the densified chitosan-Zn and chitosan membranes. The Zn 2p peaks in the XPS spectrum of the chitosan-Zn membrane clearly show the presence of Zn2+ (
We measured the N2 adsorption/desorption isotherms of the densified chitosan, porous chitosan-Zn, and densified chitosan-Zn membranes to compare their surface area (
While water plays an important role in the ion conduction of electrolytes, excess water also induces side reactions and dendrite formation on the Zn-metal anode [Ref. 9,10]. Thus, we evaluated the water-absorption ability and water content of the chitosan-Zn membrane. Different water contents (66.3-88.8 wt. %) can be achieved by soaking chitosan-Zn membranes in water or through evaporation. We hypothesized that due to the hydrophilic hydroxyl and amine groups of chitosan, the chitosan-Zn would be able to confine water molecules via hydrogen bonding, thus reducing the ratio of free water in the membrane. Indeed, differential scanning calorimetry (DSC) showed that the chitosan-Zn membranes with different water contents featured both bound water and free water (
We found the chitosan-Zn membrane serves as an excellent Zn2+ electrolyte with a high Zn2+ ionic conductivity and advantageous Zn plating behavior. The chitosan-Zn electrolytes were obtained by immersing the porous chitosan-Zn membranes in 2 M ZnSO4 aqueous solution, followed by the densifying procedure. The excellent wettability of the chitosan-Zn membrane toward ZnSO4 aqueous solution (
We applied a galvanostatic plating/stripping method to investigate the Zn plating behavior in Zn∥Zn cells using chitosan-Zn electrolytes with different water contents (34%, 57%, and 72%) and compared them with the pure aqueous electrolyte of 2 M ZnSO4. After cycling at 20 mA cm−2 and 4 mAh cm−2 for 50 cycles, we used SEM to observe the Zn plating morphology on the Zn anodes (
The deposition of hexagonal Zn platelet is because the (0002) plane of Zn has a lower surface energy (0.33 Jm−2) than other planes (e.g., 0.53 J m−2 of the (−1010) plane), which causes the preferential crystal growth of Zn in the (0002) plane, forming hexagonal platelets [Ref. 34]. The chitosan-Zn electrolyte enables fast and uniform Zn2+ conduction while also limiting ion flux perpendicular to Zn anode surface, forming parallel Zn platelets compactly stacked on the anode (
The Zn cycling reversibility of the chitosan-Zn electrolyte is evidenced by the Coulombic efficiency of the Zn-metal anode, which we investigated by cycling Zn∥chitosan-Zn∥Cu cells at 5 mA cm−2 with a capacity of 5 mAh cm−2 (
We further tested the Coulombic efficiency at high-current-density and high-capacity conditions in Zn∥Cu cells to evaluate the performance of the Zn anode made with the 57%-water-content chitosan-Zn electrolyte (which was used in all following experiments unless otherwise indicated). The Zn∥Cu cells show a high Coulombic efficiency of 99.3% for 1,300 cycles at 5 mA cm−2 with a capacity of 1 mAh cm−2 and 99.8% at 5 mA cm−2 with a capacity of 5 mAh cm−2 (
With the chitosan-Zn electrolyte, we achieved excellent cycling performance and long lifespan in symmetric Zn-metal batteries at high current densities (up to 50 mA cm−2). The symmetric Zn batteries using the chitosan-Zn electrolyte can stably cycled for up to ˜2,500 cycles at 5 mA cm−2 with capacities of 1 and 2.5 mAh cm−2 (
We examined the Zn anode surface after 1,000 cycles at 10 mA cm−2 with the chitosan-Zn electrolyte and found that the Zn maintained platelet-like morphology (
With the chitosan-Zn electrolyte, we can cycle the Zn symmetric cell at 50 mA cm−2 with a cumulative plating capacity of 10 Ah cm−2 (
To evaluate the performance of the chitosan-Zn electrolyte in full cells, we used an organic cathode material (PBQS) to couple with the Zn-metal anode. PBQS is a promising organic electrode material for aqueous Zn batteries due to its low cost, abundant resources, high reversible capacity, and good cycling stability [Ref. 38,39], as well as its biodegradable and environmentally friendly properties as one member of quinone family [Ref. 4]. Pairing the PBQS cathode (with a high PBQS mass loading of 10 mg cm−2) with the Zn-metal anode and the chitosan-Zn electrolyte, the Zn full cell shows a higher discharge/charge capacity (˜190 mAh g−1) and lower overpotential at rate capacity of 5C (1C=200 mA g−1) than the cell using aqueous electrolyte (
Aside from the high-rate and high-capacity performance, we also demonstrated the safety and sustainability of the cell using the chitosan-Zn electrolyte. As a gel electrolyte filled with aqueous solution, the chitosan-Zn electrolyte is not flammable and only shrinks and becomes soft when placed in a flame (
In conclusion, we have developed a sustainable Zn-coordinated chitosan electrolyte and demonstrate its high performance for use in Zn-metal batteries. The chitosan-Zn membrane was fabricated using a facile two-step method of Zn2+-coordination of chitosan, followed by mechanical pressing, resulting in a dense structure. The chitosan-Zn membrane displays a high mechanical strength and water bonding capability, which enables a tunable Zn2+ conductivity and controllable Zn electrodeposition morphology. With controlled water content of 57%, the chitosan-Zn electrolyte exhibits a high ionic conductivity of 72 mS cm−1 and enables a desirable parallel Zn platelet deposition morphology. As a result, the chitosan-Zn electrolyte can enable cycle at 50 mA cm−2 for >1,000 cycles with excellent reversibility and high Coulombic efficiency (99.7%). The Zn-metal full cells fabricated using the chitosan-Zn electrolyte show a high-rate performance (10-20C) and long lifespan (>400 cycles at 2C) with an areal capacity of 2.3 mAh cm−2 (cathode loading of 10 mg cm−2), better than most of the reported Zn-metal batteries. Owing to its excellent electrochemical performance, low cost, high safety, biodegradability, and facile fabrication method, the chitosan-Zn electrolyte and its design strategy paves a way for developing high-performance and sustainable biopolymer-based electrolytes for green energy-storage and -conversion devices.
Chitosan powder (>75% deacetylated) was purchased from Millipore Sigma. Zinc foil (100 mm in thickness) was purchased from MTI. Sodium hydroxide and zinc sulfate were purchased from Millipore Sigma and used directly without any treatment.
Chitosan powder (1 g) was first dissolved in 4 wt. % acetic acid aqueous solution (200 mL) by stirring overnight at room temperature to produce a 0.5 wt. % chitosan solution. A filtration process was used to remove the undissolved impurities. The obtained transparent chitosan solution was further concentrated through evaporation to obtain a viscous ˜4 wt. % chitosan solution. This chitosan solution was then drop cast on a Petri dish or cast on a PET film with a doctor blade with a solution weight of ˜0.16 g cm−2. The resulting chitosan wet film was then immediately immersed in a Zn2+-saturated NaOH solution (0.6 wt. % Zn2+ measured by inductively coupled plasma mass spectrometry [ICP-MS]) for 4 days, which was prepared by immersing excess Zn foil in 20 wt. % NaOH solution for 1 week. A porous chitosan-Zn membrane is formed by the solvent-nonsolvent exchange process, in which the acidic aqueous solution is the solvent and the NaOH aqueous solution is the nonsolvent. The resulting porous chitosan-Zn membrane was washed with excess water. A pressure of ˜5 MPa was applied to densify the porous chitosan-Zn membrane to obtain the densified chitosan-Zn membrane. The dry porous and densified chitosan-Zn membranes were freeze dried for material characterization.
The porous chitosan-Zn membrane was immersed in 2 M ZnSO4 aqueous solution overnight and then pressed at 5 MPa to densify the membrane. The resulting chitosan-Zn electrolyte was then obtained after wiping excess ZnSO4 solution off the surface of the densified membrane with a mass of m0. The water content in this electrolyte is 57% based on the ratio of m1 and m0, where m1 is the mass of chitosan-Zn electrolyte after removing water completely in vacuum oven at 100° C. The chitosan-Zn electrolyte samples with different water contents were prepared by evaporating the densified membrane (m0) in air or soaking the densified membrane in 2 M ZnSO4 solution, until membranes were obtained with masses of 0.5, 0.75, 1.25, and 1.5 m0. The calculated water content in these chitosan-Zn electrolytes was 34%, 43%, 66%, and 72%, respectively.
Zn symmetric cells were assembled using Zn foils for both the cathode and anode and either the chitosan-Zn electrolyte (which also served as the separator) or aqueous electrolyte (100 mL 2M ZnSO4) with a glass-fiber separator. The asymmetric Cu∥Zn cells were assembled using Cu foil and Zn foil as the cathode and anode, respectively. All cells were assembled in an ambient environment using CR2032 coin cells and were tested at room temperature. The galvanostatic plating/stripping profiles were measured at different areal capacities and different current densities on a NEWARE battery-testing system. The Zn plating/stripping Coulombic efficiencies were probed at different current densities with a charge-cutoff voltage of 1 V. EIS data were measured using a Biologic VMP3 electrochemical workstation at an amplitude of 10 mV at an open-circuit voltage.
Poly(benzoquinonyl sulfide) (PBQS) was synthesized following a method reported in the literature [Ref. 46]. To prepare composite electrodes, PBQS, Ketjen black (KB) carbon, and polytetrafluoroethylene (PTFE) were mixed at a mass ratio of 7:2:1 with 2 mL ethanol as the dispersant. The freestanding electrodes were cut and pressed into stainless-steel meshes (1 cm2, 100×100 mesh) and dried at 80° C. under vacuum for 12 hours before cell assembly. The areal loading of the active material was ˜10 mg cm−2.
The electrochemical performances of the composite electrodes were evaluated in a split cell by using zinc foil as the anode and chitosan-Zn electrolyte (150 mm) or 80 mL of 2 M ZnSO4 aqueous electrolyte with a glass-fiber separator (Whatman, 150 mm). Electrochemical characterization was performed with a potentiostat (VMP3, Biologic). The cells were tested under different charge/discharge rates of 1 to 20C, where 1C equals a current density of 200 mA g−1. All electrochemical tests were run at room temperature.
The morphologies of the samples were studied by SEM at 10 kV on a Hitachi SU-70 with EDS analysis at 15 kV. XPS was conducted on a Thermo ESCALAB 250. The C1s peak at 284.8 eV was used as a reference to calibrate the binding energy values of other peaks. FTIR was performed with a Thermo Nicolet NEXUS 670 FTIR with an attenuated total reflectance (ATR) accessory.
XRD was performed on a Bruker D8 Advance powder diffractometer with Cu radiation (scan rate of 2° min−1). N2 adsorption/desorption isotherms were measured on a Micromeritics ASAP 2020 Porosimeter. Specific surface area and pore size were determined by the BET and Barrett-Joyner-Halenda (BJH) methods, respectively. Tensile stress-strain curves were conducted on a tabletop model testing system (Instron, Norwood, MA, USA) with a running speed of 0.1 mm min-. DSC was performed on a TA Instruments DSC Q100. The samples are first cooled to ˜30° C. then heated to 20° C. to obtain a melting curve with a cooling/heating rate of 5° C. min−1. ICP was conducted on a PerkinElmer NexION 300D ICP-MS, where 63Cu standard solutions were used to construct a calibration curve.
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a Prices are sourced from Alibaba.
b Chitosan-Zn electrolyte with a dry mass of 90 g and a size of 1 m2 was produced from 60 g chitosan, 100 g NaOH, and 80 g ZnSO4.
Thus, examples of the present disclosure provide electrolytes that can facilitate transport of ions with wide applications in electrochemical devices, such as batteries. In particular, we have found that a biomaterial-derived chitosan-Zn electrolyte enables favorable Zn-platelet deposition due to its high mechanical strength, high Zn2+ conductivity, and water bonding capability. The chitosan-Zn electrolyte not only enables high-rate and long-life performance in zinc metal batteries, but is also biodegradable, appealing for clean and efficient energy storage.
In light of the principles and example embodiments described and illustrated herein, it will be recognized that the example embodiments can be modified in arrangement and detail without departing from such principles. Also, the foregoing discussion has focused on particular embodiments, but other configurations are also contemplated. In particular, even though expressions such as “in one embodiment”, “in another embodiment”, “in an embodiment”, “in some embodiments”, “in certain embodiments”, or the like are used herein, these phrases are meant to generally reference embodiment possibilities, and are not intended to limit the disclosure to particular embodiment configurations. As used herein, these terms may reference the same or different embodiments that are combinable into other embodiments. As a rule, any embodiment referenced herein is freely combinable with any one or more of the other embodiments referenced herein, and any number of features of different embodiments are combinable with one another, unless indicated otherwise.
Although the present disclosure has been described in considerable detail with reference to certain embodiments, one skilled in the art will appreciate that aspects of the present disclosure can be used in alternative embodiments to those described, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.
This application claims priority to U.S. Patent Application No. 63/367,706 filed Jul. 5, 2022, which hereby is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63367706 | Jul 2022 | US |
