Ultrathin reference electrode and electrochemical device including same

Abstract

A battery cell comprising an anode, a cathode and a reference electrode wherein the reference electrode is disposed between the anode and the cathode; wherein the reference electrode comprises an active material layer arranged on a current collector; and wherein the active material layer comprises lithium, a lithium aluminum alloy, sodium, a sodium potassium alloy, a sodium calcium alloy, a sodium lithium magnesium alloy, a sodium lithium aluminum alloy, a sodium lead alloy, a sodium silicon alloy, a sodium antimony alloy, or a sodium zinc alloy.

Description

Technical Field

[0001] The present disclosure relates to a thin film reference electrode, an electrochemical device including the thin film reference electrode, and a method of manufacturing the electrochemical device. Background Art

[0002] Secondary or rechargeable metal ion batteries are commonly used in many stationary and portable devices, such as those encountered in consumer electronics, automotive / motor vehicles, medical devices, machinery, robotics, and the aerospace industry. Examples of secondary or rechargeable metal ion batteries include lithium-based batteries and sodium-based batteries. In the automotive industry, metal ion batteries may be suitable for electric vehicles such as hybrid electric vehicles (HEV), battery electric vehicles (BEV), plug-in HEV, and extended-range electric vehicles (EREV). Lithium batteries are popular for a variety of reasons, including relatively high energy density, high power capacity, generally no memory effect compared to other types of rechargeable batteries, relatively low internal resistance, and low self-discharge rate when not in use. The ability of lithium batteries to cycle power repeatedly during their useful life makes them an attractive and reliable power source.

[0003] Rechargeable metal ion batteries work by reversibly transferring metal ions back and forth between a negative electrode and a positive electrode. A separator and an electrolyte are disposed between the negative and positive electrodes. The electrolyte is suitable for conducting metal ions and can be in solid (e.g., solid-state diffusion) or liquid form. During battery charging, metal ions move from the cathode (positive electrode) to the anode (negative electrode), and when the battery is discharged, the metal ions move in the opposite direction.

[0004] It may be desirable to perform electrochemical analysis of a battery or certain components of a battery during cycling. In many cases, a reference electrode is able to monitor a single potential during cycling without interfering with battery operation. Common reference electrodes include one or more gold layers (e.g., current collector layers) disposed on one or more surfaces of a porous separator substrate, for example, using a sputtering process. The current collector layer is typically a non-porous but permeable gold film. Such reference electrodes are typically expensive and require a complex manufacturing process. Therefore, there is a need to develop improved reference electrode materials and structures and methods for their manufacture to address these and other challenges. Summary of the invention

[0005] In one aspect, a battery cell is provided that includes an anode, a cathode, and a reference electrode, wherein the reference electrode is disposed between the anode and the cathode. The reference electrode includes an active material layer disposed on a current collector. The active material layer includes lithium, lithium aluminum alloy, sodium, sodium potassium alloy, sodium calcium alloy, sodium lithium magnesium alloy, sodium lithium aluminum alloy, sodium lead alloy, sodium silicon alloy, sodium antimony alloy, or sodium zinc alloy.

[0006] In another embodiment, the battery cell further includes a first separator disposed between the anode and the reference electrode, and a second separator disposed between the cathode and the reference electrode.

[0007] In another embodiment, the current collector includes copper, nickel, titanium, platinum, gold, silver, magnesium, aluminum, vanadium, alloys thereof, or combinations thereof.

[0008] In another embodiment, the thickness of the active material layer is from 10 nanometers to 3000 nanometers.

[0009] In another embodiment, the thickness of the current collector is from 10 nanometers to 1000 nanometers.

[0010] In another embodiment, the active material layer is derived from in-situ lithium electroplating on the current collector.

[0011] In another embodiment, the active material layer is deposited on the current collector before the battery cell is assembled.

[0012] In another embodiment, the active material layer includes lithium.

[0013] In another embodiment, the anode includes at least one of the following: silicon, silicon mixed with graphite, soft carbon, hard carbon, silicon oxide (SiOx, 0 < x < 2), tin, tin dioxide, or titanium dioxide.

[0014] On the other hand, a method of forming a battery cell including an anode, a cathode, and a reference electrode is provided. The reference electrode is disposed between the anode and the cathode. The reference electrode includes an active material layer disposed on a current collector. The active material layer includes lithium, a lithium-aluminum alloy, sodium, a sodium-potassium alloy, a sodium-calcium alloy, a sodium-lithium-magnesium alloy, a sodium-lithium-aluminum alloy, a sodium-lead alloy, a sodium-silicon alloy, a sodium-antimony alloy, or a sodium-zinc alloy. The method includes forming the active material layer on the current collector.

[0015] In another embodiment, the forming includes sputter deposition, thermal evaporation, or electron beam evaporation.

[0016] In another embodiment, the forming includes forming a lithium-aluminum alloy layer.

[0017] In another embodiment, the forming includes potentiostatic lithiation, galvanostatic lithiation, or electrical shorting of the current collector.

[0018] In another embodiment, the current collector includes copper, nickel, titanium, platinum, gold, silver, magnesium, aluminum, vanadium, alloys thereof, or combinations thereof.

[0019] In another embodiment, the thickness of the active material layer is from 10 nanometers to 3000 nanometers.

[0020] In another embodiment, the thickness of the current collector is from 10 nanometers to 1000 nanometers.

[0021] In another embodiment, the anode comprises at least one of the following: silicon, silicon mixed with graphite, soft carbon, hard carbon, silicon oxide (SiOx, 0 < x < 2), tin, tin dioxide, or titanium dioxide.

[0022] In another embodiment, the current collector comprises aluminum and forms an active material layer including in-situ lithiation to provide a lithium-aluminum alloy.

[0023] In another embodiment, the current collector comprises copper or nickel and forms an active material layer including in-situ lithium electroplating to provide a layer of lithium.

[0024] In another embodiment, an active material layer including sodium is formed in-situ.

[0025] When taken in conjunction with the accompanying drawings, the above and other features and advantages of the present disclosure will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features, advantages, and details appear only by way of example in the following detailed description, which refers to the accompanying drawings, in which:

[0027] Figure 1 is a schematic perspective view of an electric vehicle according to one or more embodiments, having a cut-away portion to show the battery pack assembly;

[0028] Figure 2 schematically shows an exploded perspective view of a battery cell according to one or more embodiments;

[0029] Figure 3 graphs showing the potential (volts V) of a lithium-aluminum reference electrode and a lithium reference electrode versus time (hours hr), respectively;

[0030] Figure 4 is a graph of the potential (V) of a lithium-aluminum reference electrode versus time (hr) according to one aspect; and

[0031] Figure 5 is a graph of the reference electrode potential (V) of a lithium reference electrode on in-situ electroplated copper versus time (hr) according to one aspect. DETAILED DESCRIPTION

[0032] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. It should be understood that in all the figures, corresponding reference numerals denote the same or corresponding parts and features. As used herein, the terms "anode" and "negative electrode" may be used interchangeably, and the terms "cathode" and "positive electrode" may be used interchangeably.

[0033] The present technology relates to improved electrochemical batteries (e.g., battery cells), particularly lithium-ion batteries, or more particularly lithium metal batteries, which can be used in vehicle applications. However, the present technology can also be used in other electrochemical devices, such as sodium-ion batteries, so the discussion of lithium-ion batteries herein is non-limiting.

[0034] Reference now Figure 1 , an electric vehicle 1 is shown having a high-voltage battery pack assembly 7 equipped with a battery module 2. The exemplary battery module 2 includes a plurality of electrochemical battery cells, such as metal ion batteries. In addition, the battery pack assembly 7 may include a plurality of battery modules 2. The exemplary electric vehicle 1 includes a vehicle chassis 3 and a battery tray 4. In the illustrated embodiment, the battery module 2 is attached to the battery tray 4. In addition, the battery tray 4 is attached to the vehicle chassis 3 to fix the battery pack assembly 7 to the electric vehicle 1.

[0035] The exemplary electric vehicle 1 may also include a battery disconnect unit (BDU) 5 that is connected to the battery pack assembly 7 and provides electrical communication between the battery pack assembly 7 and an electrical system (not shown) of the electric vehicle 1. The exemplary electric vehicle 1 may further include a battery cover 6 that extends around the battery module 2. The exemplary battery cover 6 may protect the battery module 2 from damage, as well as provide electrical insulation from the high voltage of the battery pack assembly 7. Figure 1 The battery pack assembly 7 shown includes a battery module 2 , a battery tray 4 , a BDU 5 and a battery cover 6 ; while the vehicle chassis 3 is not a component of the battery pack assembly 7 .

[0036] According to an exemplary embodiment, an electrochemical cell is provided that includes an anode, a cathode, and a reference electrode, wherein the reference electrode is disposed between the anode and the cathode. The reference electrode includes an active material layer disposed on a current collector; the active material layer includes lithium, lithium aluminum alloy, sodium, sodium potassium alloy, sodium calcium alloy, sodium lithium magnesium alloy, sodium lithium aluminum alloy, sodium lead alloy, sodium silicon alloy, sodium antimony alloy, or sodium zinc alloy. In some embodiments, the active material layer includes lithium or lithium aluminum alloy.

[0037] Figure 2 One embodiment of a battery cell 10 is schematically shown, which includes an anode 20, a first separator 40, a reference electrode 50, a second separator 42, and a cathode 30, which are arranged in a stack and sealed in a flexible bag 60 containing an electrolytic material 62 (electrolyte). A first negative cell tab 26 and a second positive cell tab 36 protrude from the flexible bag 60. A single arrangement of the anode 20, the first separator 40, the reference electrode 50, the second separator 42, and the cathode 30 is shown. It should be understood that different configurations of the anode 20, the first separator 40, the reference electrode 50, the second separator 42, and the cathode 30 can be used and electrically connected in the flexible bag 60 depending on the specific application of the battery cell 10.

[0038] When the anode 20 contains a relatively large amount of lithium (or sodium), the battery cell 10 can generate current during discharge through a reversible electrochemical reaction when the external circuit is closed (to connect the anode 20 and the cathode 30). The chemical potential difference between the cathode 30 and the anode 20 drives the electrons generated by the anode 20 to flow to the cathode 30 through the external circuit. The lithium ions (or sodium ions) also generated at the cathode 30 are transferred to the cathode 30 through the electrolyte 60 and the separator 42 at the same time. The electrons flow through the external circuit, and the lithium ions (or sodium ions) migrate through the separator 42 in the electrolyte 60 to the cathode 30, where they can be plated, reacted or intercalated. The current flowing through the external circuit can be utilized and directed through a load device until the lithium (or sodium) in the anode 20 is depleted and the capacity of the battery cell 10 is reduced. In lithium-ion batteries, lithium is intercalated into and / or alloyed with electrode active materials, whereas in lithium-sulfur batteries, lithium is not intercalated or alloyed but rather dissolves and migrates from the negative electrode to the positive electrode, where lithium reacts / plates during discharge and plates on the negative electrode during charge.

[0039] The battery cell 10 can be charged or re-energized by connecting an external power source to the battery cell 10 to reverse the electrochemical reactions that occur during battery discharge. The connection of the external power source to the battery cell 10 forces electrons to generate and release lithium ions (or sodium ions) from the cathode 30. The electrons flowing back to the anode 20 through the external circuit and the lithium ions (or sodium ions) carried by the electrolyte 60 through the separator 42 to the anode 20 are recombined at the anode 20 and replenished with lithium (or sodium) for consumption in the next battery discharge cycle. In this way, each discharge and charge event is considered to be a cycle in which lithium ions (or sodium ions) circulate between the cathode 30 and the anode 20.

[0040] In addition, the battery cell 10 may include various other components, although not shown here for convenience, these components are known to those skilled in the art and may be included in the battery cell 10. For example, as a non-limiting example, the battery cell 10 may include a housing, a gasket, a terminal cap, a terminal tab, a battery terminal and / or any other conventional components or materials, including between or around the anode 20, the cathode 30 and / or the separators 40, 42. As described above, the size and shape of the battery cell 10 may vary depending on the specific application for which it is designed. If required by the load device, the battery cell 10 may also be connected in series or in parallel with other similar battery cells or batteries to produce greater voltage output, energy and / or power.

[0041] Anode 20 includes an anode active material 22 disposed on an anode current collector 24. In some embodiments, Figure 2As shown, the anode current collector 24 may have a foil portion 25 that extends from the anode active material 22 to form a first cell tab 26.

[0042] The anode current collector 24 may include a metal, including copper, nickel, or an alloy thereof, stainless steel, or other suitable conductive material. The anode current collector 24 may be in the form of a foil, a slotted mesh, and / or a woven mesh. In one embodiment, the anode current collector includes copper.

[0043] The anode active material 22 may be a lithium host material. Common electrochemically active negative materials include lithium insertion materials or alloy host materials. Such materials may include carbon-containing materials, such as lithium-graphite intercalation compounds, lithium-silicon compounds, lithium-tin alloys, or lithium titanate Li 4+x Ti 5 O 12 , where 0 ≤ x ≤ 3, such as Li 4 Ti 5 O 12 (LTO). For example, the anode active material 22 may include at least one of the following: silicon, silicon mixed with graphite, soft carbon, hard carbon, silicon oxide (SiOx, 0 < x < 2), tin, tin dioxide, titanium dioxide, or a combination thereof. The lithium host material may be mixed with a polymeric binder material to provide structural integrity and, in some aspects, a conductive fine particle diluent. For example, the lithium host material may be graphite, and the polymeric binder material may be one or more of polyvinylidene fluoride (PVdF), ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid, or a combination thereof. Graphite exhibits favorable lithium intercalation and deintercalation characteristics, which helps to provide the desired energy density for the anode 20. Various forms of graphite are commercially available. The conductive diluent may be, for example, fine particles of high surface area carbon black. For sodium batteries, a suitable anode active material 22 is a sodium host material.

[0044] In some embodiments, the anode 20 may optionally include one or more of graphite, activated carbon, carbon black, hard carbon, soft carbon, graphene, silicon, tin oxide, aluminum, indium, zinc, germanium, silicon oxide, titanium oxide, lithium titanate, or a combination thereof. Non-limiting examples of silicon-containing electrochemically active materials include silicon (amorphous or crystalline), or silicon-containing binary and / or ternary alloys, such as SiSn, SiSnFe, SiSnAl, SiFeCo, etc., or a combination thereof. For example, the anode may include at least one of silicon, silicon mixed with graphite, soft carbon, hard carbon, silicon oxide (SiOx, 0 < x < 2), tin, tin dioxide, or titanium dioxide.

[0045] In other embodiments, the anode 20 can be a lithium metal electrode (LME). Metallic lithium for the negative electrode of a rechargeable battery has various potential advantages, including the highest theoretical capacity and the lowest electrochemical potential. Thus, a battery incorporating a lithium metal anode can have a higher energy density, which can potentially double the storage capacity, so the battery can be half the size but still last the same amount of time as other lithium-ion batteries.

[0046] The cathode 30 includes a cathode active material 32 disposed on a cathode current collector 34. In some embodiments, as Figure 2 shown, the cathode current collector 34 can have a foil portion 35 extending from the cathode active material 32 to form a second cell tab 36.

[0047] The cathode current collector 34 can be formed of aluminum, an aluminum alloy, or any other suitable electrically conductive material. The cathode current collector 34 can be in the form of a foil, a slotted mesh, and / or a woven mesh. In one embodiment, the cathode current collector includes aluminum.

[0048] When the cell 10 is a lithium-ion battery, the cathode active material 32 can include a lithium-containing active material, such as a layered lithium transition metal oxide. Exemplary lithium-containing active materials include spinel lithium manganese oxide (LiMn 2 O 4 ), lithium cobalt oxide (LiCoO 2 ), nickel manganese oxide spinel (Li(Ni 0.5 Mn 1.5 )O 2 ), layered nickel manganese cobalt oxide (having the general formula xLi 2 MnO 3 (1-x)LiMO 2 , where M is composed of any proportion of Ni, Mn, and / or Co). A specific example of a layered nickel-manganese oxide spinel is xLi 2 MnO 3 (1-x)Li(Ni 1 / 3 Mn 1 / 3 CO 1 / 3 )O 2 . Other exemplary lithium-containing cathode active materials include Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O 2 ), LiNiO 2 , Li x +yMn 2 -yO 4 (LMO, 0 < x < 1 and 0 < y < 0.1), lithium iron polyanion oxide, such as lithium iron phosphate (LiFePO 4 ) or lithium iron fluorophosphate (Li2 FePO 4 F, LFP) or a combination thereof. Other lithium-containing cathode active materials, such as LiNi x M 1-x O 2 (M is composed of Al, Co and / or Mg in any proportion), LiNi 1-x Co 1-y M x+y O 2 or LiMn 1.5-x Ni 0.5-y M x+y O 4 (M is composed of Al, Ti, Cr and / or Mg in any proportion), stable lithium manganese oxide spinel (Li x Mn 2-y M y O 4 , wherein M is composed of Al, Ti, Cr and / or Mg in any proportion), lithium nickel cobalt aluminum oxide (e.g. LiNi 0.8 Co 0.15 Al 0.05 O 2 or NCA), aluminum-stabilized lithium manganese oxide spinel (LixMn 2-x Al y O 4 ), lithium vanadium oxide (LiV 2 O 5 )、Li 2 MSiO 4 (M is composed of Co, Fe and / or Mn in any proportion), high-efficiency nickel-manganese-cobalt materials (HE-NMC, NMC or LiNiMnCoO 2 ), etc., or a combination thereof. "Any ratio" means that any element can be present in any amount. In another example, anion substitution can be performed in the crystal lattice of any example of the lithium transition metal active material to stabilize the crystal structure. For example, any O atom can be replaced by a F atom.

[0049] When the battery cell 10 is a sodium ion battery, the cathode active material may include a sodium-containing active material. Examples of suitable sodium-containing active materials include, but are not limited to, sodium hexacyanomanganate (Na 2 Mn[Mn(CN) 6 ]),NaVPO 4 F,NaMnO 2 ,NaFePO 4 ,Na 3 V 2 (PO 4 ) 3 ), etc., or a combination thereof.

[0050] The cathode active material can be mixed with a binder and / or a conductive filler. Suitable binders include polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), ethylene propylene diene rubber (EPDM), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), styrene-butadiene rubber carboxymethyl cellulose (SBR-CMC), polyacrylic acid (PAA), cross-linked polyacrylic acid-polyethylene imine, polyimide, polyvinyl alcohol (PVA), sodium alginate, combinations thereof, or other suitable binders. An example of a conductive filler is high surface area carbon, such as acetylene black, etc. The binder can hold the electrode material together, and the conductive filler can ensure good electronic conduction between the positive side current collector and the cathode active material particles.

[0051] In various aspects, the negative electrode 20 and the positive electrode 30 can be made by mixing the corresponding electroactive material with a polymer binder compound, a non-aqueous solvent, an optional plasticizer and optional conductive particles (if necessary) into a slurry. The slurry can be mixed or stirred and then thinly coated on a substrate by a doctor blade and / or slot die coating. The substrate can be a removable substrate, or a functional substrate, such as a collector (such as a metal grid or mesh layer) attached to one side of the electrode film. In one variation, heat or radiation can be applied to evaporate the solvent from the electrode film, leaving a solid residue. The electrode film can be further consolidated, where heat and pressure are applied to the film to sinter and calender it. In other variations, the film can be dried at a moderate temperature to form a self-supporting film. If the substrate is removable, it is removed from the electrode film and then further laminated to the collector. For either type of substrate, the remaining plasticizer can be extracted before being incorporated into the battery cell. In various aspects, solid electrodes can be formed according to alternative manufacturing methods.

[0052] The reference electrode 50 is disposed between the anode 20 and the cathode 30. The reference electrode 50 includes an active material layer 54 disposed on a current collector 52. The reference electrode 50 includes an ultra-thin current collector 52, one side of which is coated with the active material layer 54. The reference electrode 50 provides a fixed and constant electrochemical potential relative to the other electrodes in the cell.

[0053] The current collector 52 of the reference electrode 50 can be any suitable conductive material. For example, the current collector can include copper, nickel, titanium, platinum, gold, silver, magnesium, aluminum, vanadium, alloys thereof, or combinations thereof.

[0054] The current collector 52 may have a thickness of 10 nanometers (nm) to 1000 nm. For example, the current collector 52 may have a thickness of 10 nm to 500 nm, or 50 nm to 400 nm, or 100 nm to 400 nm, but the embodiment is not limited thereto.

[0055] The current collector 52 can be made using any suitable method. For example, the current collector 52 can be prepared by sputtering a suitable material onto a substrate, such as the separator materials described herein. In some embodiments, the current collector 52 can be prepared by sputtering deposition, thermal evaporation, or electron beam evaporation. In one embodiment, the current collector 52 can be prepared by roll-to-roll sputtering, such as roll-to-roll sputtering of aluminum to form an aluminum current collector.

[0056] The active material layer 54 includes lithium, lithium aluminum alloy, sodium, sodium potassium alloy, sodium calcium alloy, sodium lithium magnesium alloy, sodium lithium aluminum alloy, sodium lead alloy, sodium silicon alloy, sodium antimony alloy or sodium zinc alloy. In addition, the porous active material layer 54 may contain a conductive carbon diluent and a polymer binder. An independent electrical path to the reference electrode through the battery bag can be provided in the form of a reference electrode tab 56.

[0057] The active material layer 54 may have a thickness of 10 nm to 3000 nm. For example, the active material layer may have a thickness of 10 nm to 2000 nm, or 50 nm to 1000 nm, or 100 nm to 500 nm, but the embodiment is not limited thereto.

[0058] The active material layer 54 can be manufactured using any suitable method. In some embodiments, the active material layer 54 may be derived from in-situ lithiation and / or lithium electroplating of the current collector 52 and / or the material disposed on the current collector. For example, in-situ lithiation and / or lithium electroplating can be accomplished by constant potential lithiation, constant current lithiation, or electrical short circuiting of the current collector and / or the material disposed on the current collector. For example, the aluminum current collector 52 can be treated by constant potential lithiation, constant current lithiation, or electrical short circuiting to provide an active material layer 54 comprising a lithium aluminum alloy. For example, a copper current collector having an aluminum layer disposed thereon can be treated by constant potential lithiation, constant current lithiation, or electrical short circuiting to provide an active material layer comprising a lithium aluminum alloy. For example, a copper current collector can be treated by electrical short circuiting to provide an active material layer comprising lithium.

[0059] In the case of sodium ions, the active material layer 54 can be obtained from sodium ions obtained in situ using appropriate methods. For example, the current collector and / or the layer deposited on the current collector can be derived from potassium, calcium, lithium magnesium alloy, lithium aluminum alloy, lead, silicon, antimony, zinc, or a combination thereof. Therefore, the active material layer 54 can be prepared from sodium ions derived in situ to provide a sodium potassium alloy, a sodium calcium alloy, a sodium lithium magnesium alloy, a sodium lithium aluminum alloy, a sodium lead alloy, a sodium silicon alloy, a sodium antimony alloy, a sodium zinc alloy, or a combination thereof as an active material for a reference electrode. In some embodiments, the active material layer 54 includes sodium.

[0060] In other embodiments, the active material layer 54 can be prepared before assembling the battery cell 10. For example, a lithium aluminum alloy layer can be sputtered on the current collector, such as by roll-to-roll sputtering to form the active material layer 54. In some embodiments, the active material layer 54 can be prepared by sputtering deposition, thermal evaporation, or electron beam evaporation, for example, by applying the lithium aluminum alloy layer to the current collector 52 using these methods. In other embodiments, an active material layer including sodium, sodium potassium alloy, sodium calcium alloy, sodium lithium magnesium alloy, sodium lithium aluminum alloy, sodium lead alloy, sodium silicon alloy, sodium antimony alloy, sodium zinc alloy, or a combination thereof can be prepared before assembling the battery cell.

[0061] The first separator 40 is disposed between the cathode 30 and the reference electrode 50 to physically separate and electrically insulate the cathode 30 from the reference electrode 50. The second separator 42 is disposed between the anode 20 and the reference electrode 50 to physically separate and electrically insulate the anode 20 from the reference electrode 50.

[0062] In one embodiment, the first separator 40 , the reference electrode 50 , and the second separator 42 are fabricated as a single unitary component 58 that can be positioned between the anode 20 and the cathode 30 , thereby simplifying assembly and improving the manufacturability of the battery cell 10 .

[0063] The first and second separators 40, 42 can each be formed from one or more porous polymer layers, which can be individually formed from any of a variety of polymers. For simplicity, only one such polymer layer is shown. Each of the one or more polymer layers can be a polyolefin. Some specific examples of polyolefins are polyethylene (PE) (and variants such as HDPE, LDPE, LLDPE, and UHMWPE), polypropylene (PP), or a mixture of PE and PP. Commercially available polyolefin porous separators include those available from Celgard LLC. 2500 (single-layer polypropylene diaphragm) and 2340 (three-layer polypropylene / polyethylene / polypropylene separator). As an alternative or in addition to polyolefins, the separator may also include other polymers, such as but not limited to polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), polyamide (nylon), polyurethane, polycarbonate, polyester, polyetheretherketone (PEEK), polyethersulfone (PES), polyimide (PI), polyamideimide, polyether, polyoxymethylene (such as acetal), polybutylene terephthalate, polyethylene cyclopentaneate, polybutylene, polymethylpentene, polyolefin copolymers, propylene nitrile-butadiene-styrene copolymer (ABS), polystyrene copolymer, polymethyl methacrylate (PMMA), polysiloxane polymer (e.g., polydimethylsiloxane (PDMS)), polybenzimidazole (PBI), polybenzoxazole (PBO), polyarylene ether ketone, polyperfluorocyclobutane, polyvinylidene fluoride copolymer (e.g., PVdF-hexafluoropropylene or (PVdF-HFP)), or polyvinylidene fluoride terpolymer, polyvinyl fluoride, liquid crystal polymer (e.g., VECTRAN TM (Hoechst AG, Germany) or (DuPont, Wilmington, Del.)), polyaramide, polyphenylene ether, cellulose material, mesoporous silica or a combination thereof. The function of the separator is to electrically insulate and physically isolate the negative electrode 20 and the positive electrode 30 from the reference electrode 50. The first and second separators 40, 42 may also be permeated with a liquid electrolyte throughout the pores of the polymer layer. In some embodiments, the separators 40, 42 may also be mixed with a ceramic material, or their surfaces may be coated with a ceramic material. For example, the ceramic coating may include aluminum oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ), titanium dioxide (TiO 2 ), etc., or a combination thereof.

[0064] An electrolytic (electrolyte) material 62 that conducts lithium ions (or sodium ions) is contained within the separator 40 and is exposed to each of the cathode 30 and the anode 20 to allow lithium ions (or sodium ions) to move between the cathode 30 and the anode 20. Lithium ions (or sodium ions) deintercalated from the anode 20 during discharge or lithium ions (or sodium ions) deintercalated from the cathode 30 during charge release electrons, which flow through the current collectors 24 and 34, respectively, through an external circuit connected to a load or a charger, and then reach the opposite current collectors (34 and 24) and electrodes (30 and 20), where they reduce lithium ions (or sodium ions) to lithium metal (or sodium ions) when lithium ions (or sodium ions) are deintercalated.

[0065] For lithium-ion battery cell 10, any suitable electrolyte solution capable of conducting lithium ions between anode 20 and cathode 30 may be used. In one example, the electrolyte solution may be a non-aqueous liquid electrolyte solution that includes a lithium salt dissolved in an organic solvent or an organic solvent mixture. Non-limiting examples of lithium salts include lithium hexafluorophosphate (LiPF 6 ); lithium perchlorate (LiClO 4 ); lithium tetrachloroaluminate (LiAlCl 4 ); lithium iodide (LiI); lithium bromide (LiBr); lithium thiocyanate (LiSCN); lithium tetrafluoroborate (LiBF 4 ); Lithium difluorooxalatoborate (LiBF 2 (C 2 O 4 ))(LiODFB), lithium tetraphenylborate (LiB(C 6 H 5 ) 4 ); Lithium bis(oxalato)borate (LiB(C 2 O 4 ) 2 )(LiBOB); Lithium tetrafluorooxalate phosphate (LiPF 4 (C 2 O 4 ))(LiFOP), lithium nitrate (LiNO 3 ) lithium hexafluoroarsenate (LiAsF 6 ); lithium trifluoromethanesulfonate (LiCF 3 SO 3 ); Lithium bis(trifluoromethanesulfonyl imide) (LITFSI)(LiN(CF 3 SO 2 ) 2 ); Lithium fluorosulfonyl imide (LiN(FSO 2 ) 2 )(LIFSI); or a combination thereof. In the case of sodium ion batteries, a suitable sodium salt may be selected.

[0066] These and other similar lithium salts can be dissolved in various organic solvents, such as cyclic carbonates ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and / or fluoroethylene carbonate (FEC), linear carbonates (dimethyl carbonate (DMC), diethyl carbonate (DEC) and / or ethyl methyl carbonate (EMC)), aliphatic carboxylates (methyl formate, methyl acetate and / or methyl propionate), γ-lactones (γ-butyrolactone and / or γ-valerolactone), chain structure ethers (1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane and / or tetraglyme), cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran and / or 1,3-dioxolane) or combinations thereof. In various aspects, the electrolyte may include one or more lithium salts greater than or equal to 0.5M to less than or equal to 4.0M, such as about 1M, about 1M to 2M, or about 3M to about 4M.

[0067] For sodium-based battery cells 10, any suitable electrolyte solution capable of conducting sodium ions between anode 20 and cathode 30 may be used. In one example, the electrolyte solution may be NaPF dissolved in EC and / or DEC. 6 , but the embodiment is not limited thereto.

[0068] In addition to the electrolyte salt and the non-aqueous solvent, other additives may be included in the electrolyte solution. For example, it may be desirable to add one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), or lithium bis(oxo)borate (LiBOB) to enhance the formation of a solid electrolyte interface on the anode graphite particles. It may be necessary to add N,N-diethylaminotrimethylsilane as a cathodic protection agent. Tris(2,2,2-trifluoroethyl)phosphate may be added as LiPF 6 Stabilizer for electrolyte salt. In addition, suitable additives may be added as safety agents and / or lithium deposition accelerators.

[0069] In some embodiments, the electrolyte may be a solid electrolyte. The solid electrolyte may include one or more solid electrolyte particles, which may include one or more polymer-containing particles, oxide-containing particles, sulfide-containing particles, halide-containing particles, borate-containing particles, nitride-containing particles, hydride-containing particles, or a combination thereof. Exemplary solid electrolytes include, but are not limited to, LiTi 2 (PO 4 ) 3 ,LiGe 2 (PO 4 ) 3 ,Li 7 La 3 Zr 2 O 12 ,Li 3 xL2 / 3 -xTiO 3 ,Li 3 PO 4 ,Li 3 N,Li 4 G JZ 4 ,Li 10 G 2 S 12 ,Li 2 SP 2 S 5 ,Li 6 PS 5 Cl,Li 6 PS 5 Br,Li 6 PS 5 I,Li 3 OCl,Li 2.99 Ba 0.005 C10 or a combination thereof.

[0070] The discharge capacity C (measured in ampere-hours or Ah) of a lithium-ion (or sodium-ion) battery can be evaluated at various currents, or more commonly at various C-rates. The C-rate is often used to describe the load on a battery or the charge of a battery, i.e. the time (ampere-hours) to charge or discharge C. The C-rate has units of amperes A and is the capacity C divided by the number of hours. A C-rate of 1C means C ampere-hours of discharge in 1 hour. Other C-rates can be used to evaluate the discharge capacity, such as C / 2 (2 hour discharge), C / 6 (6 hour discharge), C / 10 (10 hour discharge), etc.

[0071] It may be desirable to perform electrochemical analysis on the electrodes of an electrochemical cell. Electrochemical analysis can calibrate control systems in HEVs and EVs, such as fast charging, lithium plating, state of charge, and power estimation. Electrodes can be analyzed using reference electrodes provided herein. Reference electrodes can monitor the potential of each positive and negative electrode as the battery cycles. Potentials can be monitored in a laboratory environment or during real-time use of a system including an electrochemical cell. For example, potentials can be detected during vehicle operation as part of conventional vehicle diagnostics. The detected potential can be used in vehicle control algorithms to improve battery performance, such as by reducing lithium plating by increasing the anode potential.

[0072] In various aspects, the present disclosure provides a reference electrode assembly and a three-electrode battery including the reference electrode assembly. The separator layer between the anode, cathode and reference electrode layers is porous so that ions can pass through during the cycle of the electrochemical cell including the reference electrode assembly. Therefore, the reference electrode assembly does not interfere with the operation of the electrochemical cell. Therefore, the reference electrode assembly contributes to a substantially uniform current distribution.

[0073] Example

[0074] Example 1

[0075] Experiments were conducted to demonstrate the in situ formation of a lithium aluminum alloy active material layer on an aluminum reference electrode. 6 The three-electrode coin cell structure was prepared by using an electrolyte system of FEC and DMC. The reference electrode was prepared in situ by lithiating the aluminum current collector of the reference electrode to 0.1 volt (V) relative to Li by linear sweep voltammetry (LSV).

[0076] like Figure 3 As shown, after two C / 10 charge-discharge cycles between 3.0 volts (V) and 4.25 V, the resulting lithium aluminum active material achieved a 400 millivolt (mV) shift relative to the lithium reference (D), where the working electrode (A), common electrode (B), and full cell (C) are shown. The lithium aluminum active material cell is shown as 100, and for reference, the lithium active material cell is shown as 200. The charge-discharge cycle was repeated for another eight cycles (a total of ten cycles) at C / 10 cycles, spanning more than 250 hours. As shown Figure 4 As shown, the lithium aluminum active material layer provides the reference electrode with measurement stability throughout the entire period.

[0077] Example 2

[0078] Experiments were performed to demonstrate the in-situ formation of a lithium active material layer to form a reference electrode. A lithium anode, a high NiNCM cathode, a reference electrode, and a LiPF 6 The three-electrode cell structure was prepared by using an electrolyte system of FEC and DMC. The reference electrode was prepared by in-situ lithium plating of a copper working electrode by constant current discharge of the cell, wherein the copper working electrode was prepared by DC sputtering a layer of copper (200 nm) on a ceramic modified diaphragm. Figure 5 As shown, after two C / 10 charge-discharge cycles between 3.0 V and 4.25 V, the resulting lithium active material achieved a 0 mV shift relative to lithium, wherein the working electrode (A), common electrode (B) and full cell (C) are shown.

[0079] The terms "one" and "an" do not indicate a limitation of quantity, but rather indicate the presence of at least one of the referenced items. The term "or" means "and / or", unless the context clearly indicates otherwise. References to "an aspect" throughout the specification mean that a particular element (e.g., feature, structure, step, or characteristic) described in conjunction with that aspect is included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it should be understood that the described elements may be combined in any suitable manner in various aspects.

[0080] When an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

[0081] Unless otherwise indicated herein, all test standards are the most recent standards in effect as of the filing date of the present application or, if priority is claimed, the filing date of the earliest priority application in which the test standards appear.

[0082] Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0083] Although the above disclosure has been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the scope thereof. In addition, many modifications may be made to adapt specific situations or materials to the teachings of the disclosure without departing from the essential scope of the disclosure. Therefore, it is intended that the disclosure is not limited to the specific embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A battery cell, comprising: An anode, a cathode, and a reference electrode, wherein the reference electrode is disposed between the anode and the cathode; wherein the reference electrode comprises an active material layer disposed on a current collector; and wherein the active material layer comprises lithium, a lithium-aluminum alloy, sodium, a sodium-potassium alloy, a sodium-calcium alloy, a sodium-lithium-magnesium alloy, a sodium-lithium-aluminum alloy, a sodium-lead alloy, a sodium-silicon alloy, a sodium-antimony alloy, or a sodium-zinc alloy.

2. The battery cell according to claim 1, further comprising a first separator disposed between the anode and the reference electrode; and a second separator disposed between the cathode and the reference electrode.

3. The battery cell according to claim 1, wherein: The current collector comprises copper, nickel, titanium, platinum, gold, silver, magnesium, aluminum, vanadium, an alloy thereof, or a combination thereof.

4. The battery cell according to claim 1, wherein, the thickness of the active material layer is from 10 nanometers to 3000 nanometers, the thickness of the current collector is from 10 nanometers to 1000 nanometers, or a combination thereof.

5. The battery cell according to claim 1, wherein, the active material layer is derived from in-situ lithium electroplating of the current collector, the active material layer is deposited on the current collector before the assembly of the battery cell, or a combination thereof.

6. The battery cell according to claim 1, wherein, the active material layer comprises lithium, the anode comprises at least one of the following: silicon, silicon mixed with graphite, soft carbon, hard carbon, silicon oxide (SiOx, 0 < x < 2), tin, tin dioxide, or titanium dioxide, or a combination thereof.

7. A method of forming a battery cell comprising an anode, a cathode, and a reference electrode, wherein the reference electrode is disposed between the anode and the cathode, wherein the reference electrode comprises an active material layer disposed on a current collector, and wherein the active material layer comprises lithium, a lithium-aluminum alloy, sodium, a sodium-potassium alloy, a sodium-calcium alloy, a sodium-lithium-magnesium alloy, a sodium-lithium-aluminum alloy, a sodium-lead alloy, a sodium-silicon alloy, a sodium-antimony alloy, or a sodium-zinc alloy, the method comprising forming an active material layer on the current collector.

8. The method according to claim 7, wherein: The forming comprises potentiostatic lithiation, galvanostatic lithiation, or electrical shorting of the current collector.

9. The method according to claim 7, wherein: The current collector comprises aluminum, and the forming comprises in-situ lithiation to provide an active material layer comprising a lithium-aluminum alloy.

10. The method according to claim 7, wherein, the current collector comprises copper or nickel, and the forming comprises in-situ lithium electroplating to provide an active material layer comprising lithium; or the forming comprises in-situ forming of an active material layer comprising sodium.

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