Surface reconstruction of a negative electrode layer

Abstract

A method of reconditioning a negative electrode layer of a secondary lithium battery is disclosed, which can include performing a reconditioning cycle to recondition a major facing surface of the negative electrode layer by eliminating at least a portion of lithium dendrites or other lithium-containing surface irregularities that have formed on the major facing surface of the negative electrode layer.

Description

Technical Field

[0001] This invention relates to surface reconstruction of the negative electrode layer. Background Technology

[0002] This disclosure relates to negative electrodes, and more particularly to systems and methods for reconstructing the surface of the negative electrode layer of a secondary lithium-ion battery pack.

[0003] A battery pack is a device that converts chemical energy into electrical energy through electrochemical reduction-oxidation (redox) reactions. In secondary or rechargeable battery packs, these electrochemical reactions are reversible, which allows the battery pack to undergo multiple charge and discharge cycles.

[0004] Secondary lithium-ion battery packs typically comprise one or more electrochemical cells that operate by reversibly transferring lithium ions between a negative electrode and a positive electrode. The negative and positive electrodes are typically disposed on opposite sides of a porous polymer separator, and each electrode is typically supported on or connected to a metal current collector. The negative and positive electrodes and the polymer separator are wetted with an ion-conducting electrolyte, which provides the medium for the conduction of lithium ions across the electrochemical cell between the negative and positive electrodes. In practice, an electrochemical potential is established between the negative and positive electrodes of the electrochemical cell by connecting the respective current collectors of the negative and positive electrodes to each other via a controllable and interruptible external circuitry.

[0005] During the discharge process of an electrochemical battery, the electrochemical potential established between the negative and positive electrodes drives a spontaneous redox reaction within the battery, releasing lithium ions and electrons at the negative electrode. The released lithium ions move from the negative to the positive electrode through the ion-conducting electrolyte, and electrons move from the negative to the positive electrode via an external circuit, generating an electric current. After the negative electrode has been partially or completely depleted of lithium, the electrochemical battery can be recharged by connecting both the negative and positive electrodes to an external power source. This drives a non-spontaneous redox reaction within the battery, releasing lithium ions and electrons from the positive electrode. During the recharging of a lithium-ion battery pack, the released lithium ions return to the negative electrode and can intercalate or embed between the crystal lattice structures of the negative electrode material, or react with the negative electrode material (e.g., alloying) to form a lithium-containing intermetallic phase. In secondary lithium metal battery packs, the released lithium ions are reduced to lithium metal and deposited on the surface of the negative electrode current collector as a substantially uniform lithium metal layer.

[0006] After repeated charging cycles, moss-like or branched lithium metal structures (commonly known as lithium dendrites) may undesirably form at the interface between the electrolyte and the negative electrode surface. Furthermore, in secondary lithium metal battery packs, the physical structure of the lithium metal layer can lead to undesirable surface irregularities. It would be desirable to determine when lithium dendrites or other surface irregularities have formed on the negative electrode surface and to develop methods to restore the negative electrode to its initial state. Summary of the Invention

[0007] A method for reconstructing the negative electrode layer of a secondary lithium-ion battery pack is disclosed. In this method, electrical parameters are measured. These electrical parameters are associated with a porous sensing layer disposed between the main orientation surface of the negative electrode layer and the opposing surface of the positive electrode layer in an electrochemical cell. The porous sensing layer comprises a conductive material. The electrical parameters are evaluated to determine whether lithium dendrites continuously extend from the main orientation surface of the negative electrode layer to the porous sensing layer. In response to a positive determination that lithium dendrites are present on the main orientation surface of the negative electrode layer, a reconstruction cycle is performed. The reconstruction cycle reconstructs the main orientation surface of the negative electrode layer and eliminates at least a portion of the lithium dendrites so that they do not continuously extend from the main orientation surface of the negative electrode layer to the porous sensing layer.

[0008] The electrical parameter can be at least one of the following: (i) the potential difference between the porous sensing layer and the negative electrode layer, or (ii) the current flowing through the porous sensing layer. In this case, a reconstruction cycle can be performed when the measured value of the potential difference between the porous sensing layer and the negative electrode layer is approximately 0 or when the measured value of the current flowing through the porous sensing layer is greater than 0.

[0009] The reconstruction cycle can be performed by at least one of the following: (i) transmitting a pulsed current between the negative electrode and the porous sensing layer and through the lithium dendrite, or (ii) applying a voltage pulse across the negative electrode and the porous sensing layer to allow current to flow through the lithium dendrite. In this case, the execution of the reconstruction cycle can generate heat within the lithium dendrite.

[0010] A rebuilding cycle can be performed by applying a discharge current to the negative electrode layer to at least partially discharge the electrochemical cell. The discharge current applied to the negative electrode layer can exhibit a pulsed current profile comprising at least two time-spaced current pulses.

[0011] In this method, the number of charge and discharge cycles experienced by the electrochemical cell can be recorded. In this case, a rebuilding cycle can be performed when the number of charge and discharge cycles experienced by the electrochemical cell exceeds a predetermined number of charge and discharge cycles.

[0012] The negative electrode layer may be primarily composed of lithium metal and may contain more than 97% by weight of lithium, or the negative electrode layer may contain electrochemically active matrix materials such as graphite or silicon.

[0013] A method for reconstructing the negative electrode layer of a secondary lithium-ion battery pack is disclosed. In this method, an electrochemical battery is cycled. The electrochemical battery includes a negative electrode layer, a positive electrode layer, and a porous separator disposed between the main orientation surface of the negative electrode layer and the opposing surface of the positive electrode layer. Cycling the electrochemical battery includes repeatedly charging and discharging the electrochemical battery by applying a charging current to the positive electrode layer and a first discharging current to the negative electrode layer, respectively. Electrical parameters associated with the electrochemical battery are measured. The electrical parameters are evaluated to determine whether a reconstruction cycle should be performed. Based on the evaluation of the electrical parameters, a reconstruction cycle is performed to reconstruct the main orientation surface of the negative electrode layer. Cycling the electrochemical battery causes lithium dendrites or lithium-containing surface irregularities to form on the main orientation surface of the negative electrode layer. The execution of the reconstruction cycle eliminates at least a portion of the lithium dendrites or lithium-containing surface irregularities on the main orientation surface of the negative electrode.

[0014] The electrical parameter may be at least one of the following: (i) the number of charge and discharge cycles of the electrochemical cell, (ii) the measured resistance of the electrochemical cell, or (iii) the measured potential difference between the negative electrode layer and the positive electrode layer.

[0015] In the method, a rebuilding cycle can be performed when (i) the number of charging and discharging cycles is greater than a predetermined number, (ii) the measured resistance is greater than a predetermined resistance value, or (iii) the measured potential difference is less than a predetermined potential difference value.

[0016] The execution of the reconstruction cycle may include applying a second discharge current to the negative electrode layer to at least partially discharge the electrochemical cell. The second discharge current may be greater than the first discharge current. The second discharge current may exhibit a pulsed current profile comprising at least two time-spaced current pulses.

[0017] A system for reconstructing the negative electrode layer of a secondary lithium-ion battery pack is disclosed. In the system, a porous sensing layer is disposed between the main orientation surface of the negative electrode layer and the opposing surface of the positive electrode layer of an electrochemical cell. The porous sensing layer comprises a conductive material. A microcontroller is electrically coupled to the porous sensing layer and the negative electrode layer. The microcontroller is configured to: (i) measure electrical parameters associated with the porous sensing layer; (ii) evaluate the electrical parameters to determine whether lithium dendrites continuously extend from the main orientation surface of the negative electrode layer to the porous sensing layer; and (iii) in response to a positive determination of the presence of lithium dendrites on the main orientation surface of the negative electrode, perform a reconstruction cycle to reconstruct the main orientation surface of the lithium metal negative electrode layer and eliminate at least a portion of the lithium dendrites such that the lithium dendrites do not continuously extend from the main orientation surface of the negative electrode layer to the porous sensing layer.

[0018] The electrical parameter can be the potential difference between the porous sensing layer and the negative electrode layer. The potential difference can be measured by the voltmeter of the microcontroller.

[0019] The electrical parameter can be the current flowing through the porous sensing layer. The current can be measured by the ammeter of the microcontroller.

[0020] The microcontroller may include memory. In this case, the microcontroller may be configured to evaluate electrical parameters by comparing them with predetermined values ​​in a lookup table stored in the microcontroller's memory.

[0021] The system may include a non-aqueous electrolyte in ion contact with the porous sensing layer, the negative electrode layer, and the positive electrode layer. A porous separator may be disposed between the negative electrode layer and the positive electrode layer. The porous separator may be wetted with the non-aqueous electrolyte.

[0022] The negative electrode layer may be primarily composed of lithium metal and may contain more than 97% by weight of lithium, or the negative electrode layer may contain electrochemically active matrix materials such as graphite or silicon.

[0023] The electrochemical cell can be hermetically sealed within a housing. In this case, the microcontroller can be physically integrated into the housing of the electrochemical cell.

[0024] The present invention discloses the following technical solutions:

[0025] 1. A method for reconstructing the negative electrode layer of a secondary lithium battery pack, the method comprising:

[0026] Electrical parameters associated with a porous sensing layer comprising a conductive material are measured between the main oriented surface of the negative electrode layer and the opposing surface of the positive electrode layer in an electrochemical cell.

[0027] The electrical parameters are evaluated to determine whether lithium dendrites continuously extend from the main orientation surface of the negative electrode layer to the porous sensing layer; and

[0028] In response to a positive determination that the lithium dendrites are present on the main orientation surface of the negative electrode layer, a reconstruction cycle is executed to reconstruct the main orientation surface of the negative electrode layer and eliminate at least a portion of the lithium dendrites so that the lithium dendrites do not extend continuously from the main orientation surface of the negative electrode layer to the porous sensing layer.

[0029] 2. The method according to technical solution 1, wherein the electrical parameter is at least one of the following:

[0030] (i) the potential difference between the porous sensing layer and the negative electrode layer, or

[0031] (ii) Current flowing through the porous sensing layer.

[0032] 3. The method according to technical solution 2 further includes:

[0033] The reconstruction cycle is executed when the measured potential difference between the porous sensing layer and the negative electrode layer is approximately 0, or when the measured current flowing through the porous sensing layer is greater than 0.

[0034] 4. The method according to technical solution 1, wherein the reconstruction cycle is performed by at least one of the following:

[0035] (i) Current is transmitted between the negative electrode and the porous sensing layer and through the lithium dendrites, or

[0036] (ii) A voltage pulse is applied across the negative electrode and the porous sensing layer to cause current to flow through the lithium dendrite.

[0037] 5. The method according to technical solution 4, wherein the execution of the reconstruction cycle generates heat within the lithium dendrite.

[0038] 6. The method according to technical solution 1, wherein the reconstruction cycle is performed by applying a discharge current to the negative electrode layer to at least partially discharge the electrochemical cell.

[0039] 7. The method according to technical solution 6, wherein the discharge current applied to the negative electrode layer exhibits a pulsed current curve comprising at least two time-spaced current pulses.

[0040] 8. The method according to technical solution 1 further includes:

[0041] Record the number of charge and discharge cycles that the electrochemical cell has undergone, and

[0042] The reconstruction cycle is performed when the number of charge and discharge cycles experienced by the electrochemical cell exceeds a predetermined number of charge and discharge cycles.

[0043] 9. The method according to technical solution 1, wherein the negative electrode layer:

[0044] It is primarily composed of lithium and contains more than 97% lithium by weight, or

[0045] Electrochemically active matrix materials containing graphite or silicon.

[0046] 10. A method for reconstructing the negative electrode layer of a secondary lithium battery pack, the method comprising:

[0047] Cycling an electrochemical cell, the electrochemical cell comprising a negative electrode layer, a positive electrode layer, and a porous separator disposed between a main facing surface of the negative electrode layer and a opposing surface of the positive electrode layer, wherein cycling the electrochemical cell comprises repeatedly charging and discharging the electrochemical cell by applying a charging current to the positive electrode layer and a first discharging current to the negative electrode layer, respectively.

[0048] Measure the electrical parameters associated with the electrochemical cell;

[0049] The electrical parameters are evaluated to determine whether a reconstruction loop should be executed; and

[0050] Based on the evaluation of the electrical parameters, the reconstruction cycle is executed to reconstruct the main orientation surface of the negative electrode layer.

[0051] The electrochemical cell cycle causes lithium dendrites or lithium-containing surface irregularities to form on the main orientation surface of the negative electrode layer.

[0052] The execution of the reconstruction cycle eliminates at least a portion of lithium dendrites or lithium-containing surface irregularities on the main orientation surface of the negative electrode.

[0053] 11. The method according to technical solution 10, wherein the electrical parameter is at least one of the following:

[0054] (i) The number of charge and discharge cycles of the electrochemical cell,

[0055] (ii) The measured resistance of the electrochemical cell, or

[0056] (iii) The measured potential difference between the negative electrode layer and the positive electrode layer.

[0057] 12. The method according to technical solution 11 further includes:

[0058] The reconstruction loop is executed when the following conditions are met:

[0059] (i) The number of charge and discharge cycles is greater than a predetermined number.

[0060] (ii) The measured resistance is greater than the predetermined resistance value, or

[0061] (iii) The measured potential difference is less than the predetermined potential difference value.

[0062] 13. The method according to technical solution 10, wherein the execution of the reconstruction cycle includes applying a second discharge current to the negative electrode layer to at least partially discharge the electrochemical cell, and wherein the second discharge current is greater than the first discharge current.

[0063] 14. The method according to technical solution 13, wherein the second discharge current exhibits a pulse current curve comprising at least two time-spaced current pulses.

[0064] 15. A system for reconstructing the negative electrode layer of a secondary lithium-ion battery pack, the system comprising:

[0065] A porous sensing layer comprising a conductive material is disposed between the main-facing surface of the negative electrode layer and the opposing surface of the positive electrode layer in an electrochemical cell; and

[0066] A microcontroller electrically coupled to the porous sensing layer and the negative electrode layer, the microcontroller being configured to:

[0067] (i) Measure the electrical parameters associated with the porous sensing layer;

[0068] (ii) Evaluate the electrical parameters to determine whether lithium dendrites continuously extend from the main orientation surface of the negative electrode layer to the porous sensing layer exist on the main orientation surface of the negative electrode layer; and

[0069] (iii) In response to a positive determination that the lithium dendrites are present on the main orientation surface of the negative electrode, a reconstruction cycle is performed to reconstruct the main orientation surface of the negative electrode layer and eliminate at least a portion of the lithium dendrites such that the lithium dendrites do not extend continuously from the main orientation surface of the negative electrode layer to the porous sensing layer.

[0070] 16. The system according to technical solution 15, wherein the electrical parameter is the potential difference between the porous sensing layer and the negative electrode layer, and wherein the potential difference is measured by the voltmeter of the microcontroller.

[0071] 17. The system according to technical solution 15, wherein the electrical parameter is the current flowing through the porous sensing layer, and wherein the current is measured by the ammeter of the microcontroller.

[0072] 18. The system according to claim 15, wherein the microcontroller includes a memory, and wherein the microcontroller is configured to evaluate the electrical parameter by comparing the electrical parameter with a predetermined value in a lookup table stored in the memory of the microcontroller.

[0073] 19. The system according to technical solution 15 further includes:

[0074] A non-aqueous electrolyte in contact with the porous sensing layer, the negative electrode layer, and the positive electrode layer; and

[0075] A porous separator is disposed between the negative electrode layer and the positive electrode layer, wherein the porous separator is wetted by the non-aqueous electrolyte.

[0076] 20. The system according to technical solution 15, wherein the negative electrode layer:

[0077] It is primarily composed of lithium and contains more than 97% lithium by weight, or

[0078] Electrochemically active matrix materials containing graphite or silicon.

[0079] The foregoing summary is not intended to represent every possible embodiment or aspect of this disclosure. Rather, the foregoing summary is intended to illustrate some novel aspects and features disclosed herein. The foregoing features and advantages, as well as other features and advantages, of this disclosure will readily become apparent from the following detailed description of representative embodiments and models for carrying out this disclosure when considered in conjunction with the accompanying drawings and appended claims. Attached Figure Description

[0080] Schematic embodiments will be described below with reference to the accompanying drawings, wherein like reference numerals denote like elements, and wherein:

[0081] Figure 1 This is a schematic side cross-sectional view of an electrochemical cell in a secondary lithium battery pack, which includes a system for reconstructing the surface of the negative electrode layer of the electrochemical cell. The system includes a porous sensing layer disposed between the negative electrode layer and the opposing positive electrode layer, and a controller electrically coupled to the porous sensing layer and the negative electrode layer.

[0082] This disclosure is susceptible to modifications and alternatives, with representative embodiments illustrated as examples in the accompanying drawings and described in detail below. The inventive step of this disclosure is not limited to the specific forms disclosed. Rather, this disclosure is intended to cover modifications, equivalents, combinations, and alternatives within the scope of the disclosure as defined by the appended claims. Detailed Implementation

[0083] The systems and methods disclosed herein can be used to reconstruct the surface of the negative electrode layer of an electrochemical cell in a secondary lithium-ion battery pack, for example by restoring the uniformity and substantially smooth profile of the negative electrode layer surface. During repeated charge and discharge cycles of the electrochemical cell, lithium dendrites and / or other surface irregularities may form on the surface of the negative electrode layer, and the systems and methods disclosed herein can be used to eliminate or mitigate at least a portion of the lithium dendrites and / or surface irregularities.

[0084] Figure 1A schematic side cross-sectional view of an electrochemical cell 10 is depicted. The electrochemical cell 10 can be combined with one or more additional electrochemical cells to form a secondary lithium metal battery pack. The electrochemical cell 10 includes a positive electrode 12, a negative electrode 14 spaced apart from the positive electrode 12, a porous separator 16 that physically and electrically isolates the positive electrode 12 and the negative electrode 14 from each other, and a non-aqueous electrolyte 18 that wets the pores of the porous separator 16 and provides an ion conduction pathway for the transfer of lithium ions between the positive electrode 12 and the negative electrode 14 within the electrochemical cell 10. The positive electrode 12 includes a positive electrode layer 20 disposed on the main surface of a positive electrode current collector 22, and the negative electrode 14 includes a negative electrode layer 24 disposed on the opposing main surface of a negative electrode current collector 26. In practice, the positive electrode current collector 22 and the negative electrode current collector 26 can be electrically coupled to a power source or load 28 via an external circuit 30.

[0085] The porous separator 16 electrically isolates the positive electrode 12 and the negative electrode 14 from each other, and includes a first main surface 32 facing the positive electrode 12 and an opposing second main surface 34 facing the negative electrode 14. The porous separator 16 exhibits an open microporous structure and may contain organic and / or inorganic materials that can physically and electrically isolate the negative electrode layer 24 from the positive electrode layer 20 while allowing free flow of ions therebetween. The porous separator 16 may include nonwoven materials, such as sheets, meshes, or mats made of oriented or randomly oriented fibers. The porous separator 16 may include microporous polymeric materials, such as microporous polyolefin membranes (membrane or film). For example, the porous separator 16 may include a single polyolefin or a combination of polyolefins, such as polyethylene (PE), polypropylene (PP), polyamide (PA), poly(tetrafluoroethylene) (PTFE), polyvinylidene fluoride (PVdF), and / or poly(vinyl chloride) (PVC). In one form, the porous separator 16 may comprise a laminate of one or more polymeric materials, such as a laminate of PE and PP. The porous spacer 16 may have a thickness of 5 µm to 30 µm and a porosity of 25% to 75%.

[0086] In the assembly, the positive electrode layer 20, the negative electrode layer 24, and the porous separator 16 are wetted by a non-aqueous electrolyte 18. The non-aqueous electrolyte 18 provides an ion conduction path through the electrochemical cell 10 between the positive electrode layer 20 and the negative electrode layer 24. Therefore, the non-aqueous electrolyte 18 may contain materials that can pass through the porous separator 16 and effectively conduct lithium ions between the positive electrode layer 20 and the negative electrode layer 24 during the operation of the electrochemical cell 10. For example, the non-aqueous electrolyte 18 may comprise a liquid electrolyte solution comprising a lithium salt dissolved or ionized in a non-aqueous aprotic organic solvent or a mixture of non-aqueous aprotic organic solvents. Lithium salts that can be used to prepare the electrolyte include LiClO4, LiAlCl4, LiI, LiBr, LiSCN, LiBF4, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiPF6, and combinations thereof. The non-aqueous aprotic organic solvent for dissolving lithium salts can be cyclic carbonates (i.e., ethylene carbonate, propylene carbonate), acyclic carbonates (i.e., dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate), aliphatic carboxylic acid esters (i.e., methyl formate, methyl acetate, methyl propionate), γ-lactones (i.e., γ-butyrolactone, γ-valerolactone), acyclic ethers (i.e., 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (i.e., tetrahydrofuran, 2-methyltetrahydrofuran), or combinations thereof. As another example, the non-aqueous electrolyte 18 may include a gel or plasticized polymer electrolyte. In this case, the non-aqueous electrolyte 18 may include a polymer matrix material impregnated with a non-aqueous liquid electrolyte solution. Examples of polymer matrix materials include poly(vinylidene fluoride) (PVdF), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(ethylene oxide) (PEO), polyacrylate, and poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP).

[0087] A positive electrode layer 20 is disposed on a positive electrode current collector 22 and includes a main surface 36 facing the porous separator 16 and facing the negative electrode 14. The positive electrode layer 20 may contain one or more electrochemically active materials capable of reversibly redox reactions with lithium, such as materials capable of lithium intercalation and deintercalation, alloying and dealloying, or plating and stripping. The electrochemically active material of the positive electrode layer 20 may be blended with a polymer binder to provide structural integrity to the positive electrode layer 20. Examples of polymer binders include polyvinylidene fluoride (PVdF), ethylene propylene diene monomer (EPDM) rubber, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid, and mixtures thereof. Optionally, the positive electrode layer 20 may include conductive material particles, which may contain, for example, extremely fine particles of high surface area carbon black. One or more electrochemically active materials may constitute 50% to 90% by weight of the positive electrode layer 20, the polymer binder may constitute 5% to 30% by weight of the positive electrode layer 20, and the conductive material may constitute 5% to 40% by weight of the positive electrode layer 20.

[0088] The negative electrode layer 24 is disposed on the negative electrode current collector 26 and includes a main facing surface 38 facing the porous separator 16 and facing the positive electrode 12. The negative electrode layer 24 may have a thickness of 5 micrometers to 600 micrometers.

[0089] In various aspects, the negative electrode layer 24 may comprise an electrochemically active matrix material capable of undergoing a reversible redox reaction with lithium during the operation of the electrochemical cell 10. For example, the negative electrode layer 24 may comprise a material capable of reversible insertion or intercalation of lithium ions or capable of reacting with lithium to form a lithium-containing intermetallic compound. Examples of electrochemically active matrix materials for the negative electrode layer 24 include carbon-based materials (e.g., graphite, activated carbon, carbon black, and / or graphene), silicon, silicon-based alloys and / or composites, tin oxides, aluminum, indium, zinc, germanium, silicon oxides, titanium oxides, and / or lithium titanate. In embodiments where the negative electrode layer 24 comprises an electrochemically active matrix material, the matrix material may be blended with a polymer binder to provide structural integrity to the negative electrode layer 24. Examples of polymer binders include polyvinylidene fluoride (PVdF), ethylene propylene diene monomer (EPDM) rubber, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid, and mixtures thereof. The negative electrode layer 24 may optionally comprise conductive material particles, which may comprise, for example, extremely fine particles of high surface area carbon black.

[0090] In other respects, the negative electrode layer 24 may comprise a lithium metal layer. For example, the negative electrode layer 24 may comprise a lithium metal alloy or may consist essentially of lithium (Li) metal. In either case, the negative electrode layer 24 may comprise more than 97% by weight of lithium, or more preferably more than 99% by weight of lithium.

[0091] The positive electrode current collector 22 and the negative electrode current collector 26 may each comprise a material (e.g., a metallic material) capable of collecting and reversibly transporting free electrons to or from their respective electrode layers 20, 24. The positive electrode current collector 22 and the negative electrode current collector 26 may each be in the form of a thin, flexible porous or non-porous conductive metallic substrate. As used herein, the term "metal" refers to a material primarily comprising one or more metals. Therefore, a metallic material may comprise a single metal, more than one metal (in alloy or other forms), or one or more metals in elemental or compound form, and one or more other non-metallic components. For example, the positive electrode current collector 22 and the negative electrode current collector 26 may comprise conductive metals or metal alloys, such as transition metals or alloys thereof. In various aspects, the positive electrode current collector 22 may comprise an aluminum (Al), nickel (Ni), or iron (Fe) alloy (e.g., stainless steel), and the negative electrode current collector 26 may comprise a copper (Cu), nickel (Ni), iron (Fe) alloy (e.g., stainless steel), or titanium (Ti). Other conductive metallic materials may, of course, be used if desired.

[0092] A system 40 for reconstructing the primary orientation surface 38 of a negative electrode layer 24 is associated with and at least partially incorporated into the physical structure of an electrochemical cell 10. The system 40 includes an electronic control unit or microcontroller 42 and a porous sensing layer 44 disposed between the primary orientation surface 38 of the negative electrode layer 24 and the opposing surface 36 of the positive electrode layer 20. The porous sensing layer 44 is electrically coupled to the microcontroller 42, for example, via a first electrical connector 46. The negative electrode layer 24 is electrically coupled to the microcontroller 42, for example, via a second electrical connector 52. The second electrical connector 52 may be in the form of a physical and electrical connection between the negative electrode current collector 26 and the microcontroller 42. The positive electrode layer 20 may be electrically coupled to the microcontroller 42, for example, via a third electrical connector 54. The third electrical connector 54 may be in the form of a physical and electrical connection between the positive electrode current collector 22 and the microcontroller 42.

[0093] The porous sensing layer 44 is configured to provide information to a microcontroller 42, which can be interpreted by the microcontroller 42 to diagnose certain conditions within the electrochemical cell 10 without interfering with the operation of the electrochemical cell 10, particularly without inhibiting the free flow of ions between the positive electrode layer 20 and the negative electrode layer 24. The porous sensing layer 44 comprises at least one conductive material and may extend in a substantially continuous layer between the porous separator 16 and the main facing surface 38 of the negative electrode layer 24. In various aspects, the porous sensing layer 44 may be comparable in area to the facing surface 38 of the negative electrode layer 24. In the porous sensing layer 44, the at least one conductive material may be combined with one or more additional materials, which may, for example, facilitate the deposition or adhesion of the porous sensing layer 44 on the main surface 34 of the porous separator 16. The conductive material of the porous sensing layer 44 may comprise or consist substantially of at least one of nickel, copper, titanium, silver, gold, carbon, or aluminum. In practice, the pores of the porous sensing layer 44 may be wetted by a non-aqueous electrolyte 18. Without taking into account the weight of the non-aqueous electrolyte 18 within the pores of the porous sensing layer 44, the conductive material may constitute 50% to 100% by weight of the porous sensing layer 44, and more preferably greater than 90% by weight. The porous sensing layer 44 may have a thickness of 10 nanometers to 1 micrometer, or more preferably 25 nanometers to 200 nanometers. The thickness and density of the porous sensing layer 44 may be selected such that the porous sensing layer 44 is sufficiently thick and dense to form at least one continuous conductive path through it without inhibiting the free flow of lithium ions.

[0094] The porous sensing layer 44 is electrically isolated from the positive electrode layer 20 and the negative electrode layer 24. In various aspects, the porous sensing layer 44 can be electrically isolated from the positive electrode layer 20 and the negative electrode layer 24 by incorporating it into the structure of the porous separator 16. In other aspects, the porous sensing layer 44 can be disposed between the porous separator 16 and the main orientation surface 38 of the negative electrode layer 24, for example, by being disposed on the adjacent main surface 34 of the negative electrode layer 24 of the porous separator 16. In this case, a buffer layer 48 can be disposed on the main surface 34 of the porous separator 16 above the porous sensing layer 44, and the buffer layer 48 can electrically isolate the porous sensing layer 44 from the main orientation surface 38 of the negative electrode layer 24 during the operation of the electrochemical cell 10.

[0095] When included in the electrochemical cell 10, the buffer layer 48 is porous and configured to electrically isolate the porous sensing layer 44 from the main facing surface 38 of the negative electrode layer 24 without inhibiting the free flow of lithium ions through it. The buffer layer 48 may comprise or consist substantially of at least one electrically insulating material. In various aspects, the electrically insulating material of the buffer layer 48 may comprise at least one of electrically insulating ceramic materials (e.g., Al2O3, SiO2, ZrO2, TiO2, ZnO, Ta2O5, La2O5, HfO, lithium-lanthanum-zirconium oxide (Li-La-Zr-O) or zeolite), electrically insulating polymer materials (e.g., polytetrafluoroethylene), electrically insulating composite materials (e.g., aluminum alkoxide, zirconium alkoxide, titanium alkoxide), and / or diamond-like carbon. In the buffer layer 48, the electrically insulating material may be combined with one or more additional materials that may facilitate, for example, the deposition or adhesion of the buffer layer 48 on the main surface 34 of the porous separator 16 above the porous sensing layer 44. In all respects, the electrical insulating material of the buffer layer 48 may be made of the same material as the porous separator 16. In practice, the pores of the buffer layer 48 may be wetted by the non-aqueous electrolyte 18. Without taking into account the weight of the non-aqueous electrolyte 18 in the pores of the buffer layer 48, the electrical insulating material may constitute 50% to 100% by weight of the buffer layer 48, preferably more than 90% by weight of the buffer layer 48.

[0096] The microcontroller 42 is configured to operate in at least two modes: a monitoring mode and a reconstruction mode. In monitoring mode, the microcontroller 42 continuously, periodically, or intermittently measures or monitors electrical parameters associated with the electrochemical cell 10 and evaluates these parameters to determine whether to switch to reconstruction mode and perform a reconstruction cycle. The reconstruction cycle performed by the microcontroller 42 in reconstruction mode effectively reconstructs the main orientation surface 38 of the negative electrode layer 24 by restoring the uniformity and substantially smooth contour of the main orientation surface 38. During repeated cycles (charge and discharge) of the electrochemical cell 10, one or more lithium dendrites 50 or other surface irregularities may form on the main orientation surface 38 of the negative electrode layer 24. In response to the formation of lithium dendrites 50 or other surface irregularities on the main orientation surface 38 of the negative electrode layer 24, the microcontroller 42 may perform a reconstruction cycle to effectively eliminate or reduce the size of the lithium dendrites 50 or surface irregularities.

[0097] Microcontroller 42 may be in the form of an integrated circuit, including a central processing unit (CPU), memory (non-volatile memory and read / write memory), and one or more input / output (I / O) peripherals (not shown). The I / O peripherals of microcontroller 42 are configured to sense or measure one or more electrical parameters associated with electrochemical cell 10 when microcontroller 42 is operating in monitoring mode and to perform reconstruction cycle tasks when microcontroller 42 is operating in reconstruction mode. For example, microcontroller 42 may include one or more sensors, such as voltage sensors (voltmeters), current sensors (ammeters), and / or ohmmeters. Microcontroller 42 may include one or more electrical switches that can be used to control current flow in one or more circuits associated with electrochemical cell 10. Microcontroller 42 may be associated with electrochemical cell 10, for example, by physically incorporating (hermetically sealed) within a housing or casing (not shown) of electrochemical cell 10. In other embodiments, microcontroller 42 may be part of an external control device (not shown) associated with a lithium metal battery pack or another host. Power for operating microcontroller 42 may be derived from electrochemical cell 10 itself or from another power source (if desired).

[0098] When the microcontroller is running in monitoring mode, the microcontroller 42 can measure (and / or record) and evaluate one or more electrical parameters associated with the electrochemical cell 10.

[0099] In various aspects, when the microcontroller 42 operates in monitoring mode, it can measure and evaluate one or more electrical parameters associated with the electrochemical cell 10 to determine whether lithium dendrites 50 have formed on the main orientation surface 38 of the negative electrode layer 24, continuously extending from the main orientation surface 38 of the negative electrode layer 24 to the porous sensing layer 44. When a positive determination is made regarding the formation of lithium dendrites 50, the microcontroller 42 can switch to reconstruction mode. For example, the microcontroller 42 can measure the potential difference between the porous sensing layer 44 and the negative electrode layer 24 (e.g., via the first and second electrical connectors 46, 52), and evaluate the measured potential difference to determine whether lithium dendrites 50 have formed on the main orientation surface 38 of the negative electrode layer 24, continuously extending from the main orientation surface 38 of the negative electrode layer 24 to the porous sensing layer 44. If the measured potential difference between the porous sensing layer 44 and the negative electrode layer 24 is positive (i.e., > 0), the microcontroller 42 can determine that no lithium dendrites 50 exist and can continue operating in monitoring mode. If the measured potential difference between the porous sensing layer 44 and the negative electrode layer 24 is approximately zero (0), the microcontroller 42 can positively determine that there is a lithium dendrite 50 on the main orientation surface 38 of the negative electrode layer 24 that extends continuously from the main orientation surface 38 of the negative electrode layer 24 to the porous sensing layer 44. In this case, the microcontroller 42 can switch to reconstruction mode and execute a reconstruction cycle.

[0100] As another example, the microcontroller 42 can measure the current flowing through the porous sensing layer 44 (e.g., via the first electrical connector 46). The microcontroller 42 can evaluate the measured current to determine whether a lithium dendrite 50 has been formed on the main orientation surface 38 of the negative electrode layer 24, extending continuously from the main orientation surface 38 of the negative electrode layer 24 to the porous sensing layer 44. The formation of the lithium dendrite 50 extending continuously from the main orientation surface 38 of the negative electrode layer 24 to the porous sensing layer 44 will effectively complete the circuit between the negative electrode layer 24 and the porous sensing layer 44, and thus provide a path for the current to flow through the porous sensing layer 44. Therefore, if the measured current flowing through the porous sensing layer 44 is approximately zero (0), the microcontroller 42 can determine that no lithium dendrite 50 exists and can continue to operate in monitoring mode. Alternatively, if the measured current flowing through the porous sensing layer 44 is positive (i.e., > 0), the microcontroller 42 can positively determine that there is a lithium dendrite 50 on the main orientation surface 38 of the negative electrode layer 24 that extends continuously from the main orientation surface 38 of the negative electrode layer 24 to the porous sensing layer 44. In this case, the microcontroller 42 can switch to reconstruction mode and execute a reconstruction cycle.

[0101] In other respects, when the microcontroller 42 operates in monitoring mode, it can measure (and / or record) and evaluate one or more electrical parameters associated with the electrochemical cell 10 to determine whether to switch to reconstruction mode, regardless of the presence of lithium dendrites 50 on the main orientation surface 38 of the negative electrode layer 24. For example, the microcontroller 42 can maintain a record of the number of charge and discharge cycles experienced by the electrochemical cell 10 and can switch to reconstruction mode if the recorded number of charge and discharge cycles is greater than or equal to a predetermined number of charge and discharge cycles, which can be stored in the memory of the microcontroller 42 for comparison. As another example, the microcontroller 42 can measure the resistance of the electrochemical cell 10 and / or measure the potential difference between the negative electrode layer 24 and the positive electrode layer 20 (e.g., via the second electrical connector 52 and the third electrical connector 54), and if the microcontroller 42 positively determines that the measured resistance of the electrochemical cell 10 is greater than a predetermined resistance value and / or the measured potential difference between the negative electrode layer 24 and the positive electrode layer 20 is less than a predetermined potential difference value, it switches to reconstruction mode operation. The recorded charge and discharge cycle counts and / or measured resistance values ​​and / or potential difference values ​​that may cause the microcontroller 42 to switch to reconstruction mode operation can be predetermined in a laboratory environment during the calibration process of the electrochemical cell 10 and can be stored in the memory of the microcontroller 42 for comparison. Other electrical parameters that can be measured and evaluated by the microcontroller 42 to determine whether to switch to rebuild mode operation may include the open-circuit voltage of the electrochemical cell 10 and / or the rate at which the open-circuit voltage of the electrochemical cell 10 decays to the equilibrium voltage, as well as the microcontroller 42's identification of any inconsistencies or variations in the measured electrochemical potential of the electrochemical cell 10. These electrical parameters can be evaluated by the microcontroller 42 by comparing them with data stored in the microcontroller 42's memory.

[0102] Once switched to reconstruction mode, the microcontroller 42 executes a reconstruction cycle. During the reconstruction cycle, the uniformity and substantially smooth profile of the main orientation surface 38 of the negative electrode layer 24 are restored. For example, the reconstruction cycle can effectively eliminate at least a portion of the lithium dendrites 50 or surface irregularities that have formed on the main orientation surface 38 of the negative electrode layer 24. In various aspects, the reconstruction cycle can eliminate or reduce the size of the lithium dendrites 50 or surface irregularities, even if the lithium dendrites 50 or surface irregularities have not yet grown sufficiently away from the negative electrode layer 24 and into physical contact with the porous sensing layer 44.

[0103] In the case where at least one aspect of a lithium dendrite 50 extending continuously from the main orientation surface 38 of the negative electrode layer 24 to the porous sensing layer 44 has been formed on the main orientation surface 38 of the negative electrode layer 24, the execution of the reconstruction cycle may include: (i) transferring current between the negative electrode layer 24 and the porous sensing layer 44 and through the lithium dendrite 50 (e.g., via the first electrical connector 46 and the second electrical connector 52), or (ii) applying a potential difference across the negative electrode layer 24 and the porous sensing layer 44 (e.g., via the first electrical connector 46 and the second electrical connector 52) to allow current to flow through the lithium dendrite 50. Unintentionally, it is believed that allowing current to pass through the lithium dendrite 50 at a relatively high current density can effectively reconstruct the main orientation surface 38 of the negative electrode layer 24 by generating heat within the lithium dendrite 50 (thereby melting and / or dissolving or dissociating lithium in the lithium dendrite 50 into the surrounding non-aqueous electrolyte 18).

[0104] During reconstruction cycling, the magnitude of the current transported between the negative electrode layer 24 and the porous sensing layer 44 (and through the lithium dendrite 50) can be relatively small, for example, compared to the current flowing between the positive electrode layer 20 and the negative electrode layer 24 during operation of the electrochemical cell 10 and / or flowing through the lithium dendrite 50 during normal operation of the electrochemical cell 10. However, due to the inherently small diameter of the lithium dendrite 50, the local current flowing through the lithium dendrite 50 during reconstruction cycling may exhibit a relatively high current density (compared to the current density flowing simultaneously through the negative electrode layer 24 and the porous sensing layer 44). The magnitude of the current transported between the negative electrode layer 24 and the porous sensing layer 44 (and through the lithium dendrite 50) during reconstruction cycling can be chosen such that the resulting current density in the lithium dendrite 50 is 1 µA / cm². 2 ) to 1 mA / cm² 2 In various aspects, the current transmitted between the negative electrode layer 24 and the porous sensing layer 44 (and through the lithium dendrite 50) during the execution of the reconstruction cycle can be in the form of pulsed current. The current can exhibit a pulsed current profile comprising one or more current pulses, each current pulse having a duration of 1 second to 200 seconds. The number and duration of the current pulses applied during the reconstruction cycle can be based on the values ​​of electrical parameters measured, recorded, and / or evaluated associated with the electrochemical cell 10, and can be predetermined in a laboratory setting and stored in the memory of the microcontroller 42 during the calibration of the electrochemical cell 10.

[0105] The potential difference applied across the negative electrode layer 24 and the porous sensing layer 44 during the execution of the reconstruction cycle can be based on the conductive material of the porous sensing layer 44. For example, the potential difference applied across the negative electrode layer 24 and the porous sensing layer 44 during the reconstruction cycle can be selected to match the equilibrium potential of the conductive material of the porous sensing layer 44. In various aspects, the potential difference applied across the negative electrode layer 24 and the porous sensing layer 44 during the reconstruction cycle can be in the form of voltage pulses. Voltage pulses can exhibit a pulse voltage profile comprising one or more voltage pulses, wherein each voltage pulse has a duration of 1 second to 200 seconds. The number and duration of voltage pulses applied during the reconstruction cycle can be based on the values ​​of electrical parameters measured, recorded, and / or evaluated associated with the electrochemical cell 10, and can be predetermined in a laboratory setting and stored in the memory of the microcontroller 42 during the calibration of the electrochemical cell 10.

[0106] When no lithium dendrites 50 are formed on the main orientation surface 38 of the negative electrode layer 24 extending continuously from the main orientation surface 38 of the negative electrode layer 24 to the porous sensing layer 44, the execution of the reconstruction cycle may include applying a discharge current to the electrochemical cell 10 (e.g., to the negative electrode layer 24) to at least partially discharge the electrochemical cell 10. Unintentionally, it is believed that applying a discharge current to the electrochemical cell 10 at relatively high C-rates or relatively high current densities can effectively reconstruct the main orientation surface 38 of the negative electrode layer 24 by preferentially stripping lithium metal from one or more lithium dendrites 50 or from the portion of the surface irregularity extending furthest from the main orientation surface 38 of the negative electrode layer 24 (or from the negative electrode current collector 26).

[0107] During the reconstruction cycle, the discharge current applied to the electrochemical cell 10 can be in the form of a continuous or pulsed discharge current with a relatively high C-rate or current density (i.e., higher than the C-rate or current density typically occurring during the discharge of the electrochemical cell 10). For example, the discharge current applied to the electrochemical cell 10 can be equivalent to a C-rate of 1 C to 10 C and / or can exhibit 4 mA / cm². 2 Up to 40 mA / cm 2 The current density. In various aspects, a discharge current can be applied to the electrochemical cell 10 for a sufficient duration to allow the electrochemical cell 10 to reach a state of charge (SOC) of less than 3% or to achieve complete discharge (0% SOC). In various aspects, during the rebuild cycle, the potential difference (or the current flowing through the porous sensing layer 44) between the porous sensing layer 44 and the negative electrode layer 24 can be measured continuously or intermittently by the microcontroller 42. In this case, a discharge current can be applied to the electrochemical cell 10 until the measured potential difference is positive (i.e., >0) and / or the measured current is approximately zero (0).

[0108] The discharge current applied to the electrochemical cell 10 can exhibit a constant current curve or a pulsed current curve including at least two current pulses. In the aspect where the discharge current exhibits a constant current curve, the discharge current can be continuously applied to the electrochemical cell 10, and the current density of the discharge current can be constant or gradually increase over time. In the aspect where the discharge current exhibits a pulsed current curve, the at least two discharge current pulses can be applied sequentially. In other aspects, a charging current can be applied to the electrochemical cell 10 between the at least two discharge current pulses. The microcontroller 42 can determine whether to apply an intermediate charging current to the electrochemical cell 10 between the at least two discharge current pulses based on the measured or calculated state of charge (SOC) of the electrochemical cell 10.

[0109] After the rebuild cycle is executed, the microcontroller 42 can return to monitoring mode.

[0110] The reconstruction cycle of this disclosure can be performed as needed by the microcontroller 42 based on previous calibration experiments and / or on real-time monitoring of various electrical parameters of the electrochemical cell 10. Furthermore, the reconstruction cycle of this disclosure can be performed in situ without stopping the electrochemical cell 10 (or the entire battery pack) and without requiring the use of external monitoring or control equipment.

[0111] These and other benefits will be readily apparent to those skilled in the art from the foregoing disclosure.

[0112] While some best practices and other embodiments have been described in detail, various alternative designs and implementations exist for practicing the teachings as defined in the appended claims. Those skilled in the art will recognize that modifications can be made to the disclosed embodiments without departing from the scope of this disclosure. Furthermore, this concept explicitly includes combinations and sub-combinations of the stated elements and features. The detailed description and accompanying drawings are supportive and descriptive of the teachings, the scope of which is defined only by the claims.

Claims

1. A method for reconstructing the negative electrode layer of a secondary lithium battery pack, the method comprising: Measure electrical parameters associated with a porous sensing layer disposed between the main facing surface of the negative electrode layer and the opposite surface of the positive electrode layer in an electrochemical cell, the electrical parameters being at least one of (i) the potential difference between the porous sensing layer and the negative electrode layer or (ii) the current flowing through the porous sensing layer, the porous sensing layer comprising a conductive material and disposed on the main surface of the negative electrode layer adjacent to a porous separator, and a buffer layer disposed above the porous sensing layer to electrically isolate the porous sensing layer from the main facing surface of the negative electrode layer during operation of the electrochemical cell; The electrical parameters are evaluated to determine whether lithium dendrites exist on the main orientation surface of the negative electrode layer, extending continuously from the main orientation surface of the negative electrode layer to the porous sensing layer. and In response to a positive determination that the lithium dendrites are present on the main orientation surface of the negative electrode layer, a reconstruction cycle is performed to reconstruct the main orientation surface of the negative electrode layer and eliminate at least a portion of the lithium dendrites such that the lithium dendrites do not extend continuously from the main orientation surface of the negative electrode layer to the porous sensing layer, wherein the reconstruction cycle is performed by (i) transmitting current between the negative electrode and the porous sensing layer and through the lithium dendrites or (ii) applying a voltage pulse across the negative electrode and the porous sensing layer such that current flows through the lithium dendrites.

2. The method according to claim 1, further comprising: The reconstruction cycle is executed when the measured value of the potential difference between the porous sensing layer and the negative electrode layer is 0, or when the measured value of the current flowing through the porous sensing layer is greater than 0.

3. The method of claim 1, wherein the execution of the reconstruction cycle generates heat within the lithium dendrites.

4. The method of claim 1, wherein the reconstruction cycle is performed by applying a discharge current to the negative electrode layer to at least partially discharge the electrochemical cell.

5. The method of claim 4, wherein the discharge current applied to the negative electrode layer exhibits a pulsed current profile comprising at least two time-spaced current pulses.

6. The method of claim 1, further comprising: Record the number of charge and discharge cycles that the electrochemical cell has undergone, and The reconstruction cycle is performed when the number of charge and discharge cycles experienced by the electrochemical cell exceeds a predetermined number of charge and discharge cycles.

7. The method according to claim 1, wherein the negative electrode layer: It is primarily composed of lithium and contains more than 97% lithium by weight, or Electrochemically active matrix materials containing graphite or silicon.

8. A system for rebuilding the negative electrode layer of a secondary lithium battery pack, the system comprising: A porous sensing layer is disposed between the main facing surface of the negative electrode layer and the opposite surface of the positive electrode layer in an electrochemical cell. The porous sensing layer contains a conductive material and is disposed on the main surface of the negative electrode layer adjacent to the porous separator. A buffer layer is disposed above the porous sensing layer to electrically isolate the porous sensing layer from the main facing surface of the negative electrode layer during the operation of the electrochemical cell. and A microcontroller electrically coupled to the porous sensing layer and the negative electrode layer, the microcontroller being configured to: (i) Measure an electrical parameter associated with the porous sensing layer, wherein the electrical parameter is a potential difference between the porous sensing layer and the negative electrode layer, and wherein the potential difference is measured by a voltmeter of the microcontroller, and / or the electrical parameter is a current flowing through the porous sensing layer, and wherein the current is measured by a galvanometer of the microcontroller. (ii) Evaluate the electrical parameters to determine whether there are lithium dendrites extending continuously from the main orientation surface of the negative electrode layer to the porous sensing layer on the main orientation surface of the negative electrode layer; and (iii) In response to a positive determination that the lithium dendrites are present on the main orientation surface of the negative electrode layer, a reconstruction cycle is performed to reconstruct the main orientation surface of the negative electrode layer and eliminate at least a portion of the lithium dendrites such that the lithium dendrites do not extend continuously from the main orientation surface of the negative electrode layer to the porous sensing layer, wherein the reconstruction cycle is performed by (i) transmitting current between the negative electrode and the porous sensing layer and through the lithium dendrites or (ii) applying a voltage pulse across the negative electrode and the porous sensing layer such that current flows through the lithium dendrites.

9. The system of claim 8, wherein the microcontroller includes a memory, and wherein the microcontroller is configured to evaluate the electrical parameter by comparing the electrical parameter with a predetermined value in a lookup table stored in the memory of the microcontroller.

10. The system of claim 8, further comprising: A non-aqueous electrolyte that is in ion contact with the porous sensing layer, the negative electrode layer, and the positive electrode layer; and The porous separator is wetted by the non-aqueous electrolyte.

11. The system of claim 8, wherein the negative electrode layer: It is primarily composed of lithium and contains more than 97% lithium by weight, or Electrochemically active matrix materials containing graphite or silicon.

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