Patent Application
20210242550
The present subject matter relates generally to electrochemical cells. In particular, the present subject matter relates to methods for multi-electrolyte activation and refurbishment of an electrochemical cell and structures, such as sacrificial and/or reusable features that facilitate the method, as well as an electrochemical cell that includes the structures for optimizing and/or refurbishing the electrochemical cell, as well as an electrochemical cell that includes electrodes that have been optimized for a particular use with a unique electrode-electrolyte interphase (EEI), as well as the EEI-optimized electrodes themselves.
Electrochemical cells may be stored and used in varying environmental conditions. Some of the environmental conditions may be extreme, such as high or low temperatures and high or low pressures. Usage conditions may also be extreme, such as rapid charge/discharge cycling and/or subjecting a cell to large discharge depths. In these conditions, cell performance or useful life may be diminished, in part due to the passivation or other modes of degradation of the electrode, such as loss of active materials to dissolution, loss of electrical contact, or any other mode(s) of degradation known to those of skill in the art.
A description of the present subject matter including various embodiments thereof is presented with reference to the accompanying drawings, the description not meaning to be considered limiting in any matter, wherein:
The methods and structures discussed herein and shown in the drawings are for multi-electrolyte activation or refurbishment of an electrochemical cell. Methods described herein generally describe introducing a first electrolyte into a cell that will, upon activation, electrochemically decompose electrolyte components onto an electrode surface to create an electrode-electrolyte interphase (EEI). Once the EEI is created, either directly after the EEI is created during activation or at the end of the useful life of the first electrolyte, at least a portion of the first electrolyte may be extracted so that a second electrolyte can be introduced into the electrochemical cell. The second electrolyte can interact with the EEI to efficiently perform and/or to optimize performance of the electrochemical cell over a broader range of conditions than if the second electrolyte were interacting with a bare electrode.
Some of these conditions include operation and storage in extreme temperatures, such as temperatures greater than about 60 degrees Celsius or below minus 20 degrees Celsius, high currents and/or voltages, large discharge depths, rapid charge/discharge cycling, extended storage shelf-life, and/or reduced self-discharge. In some cells, even small increases in temperature will have a major influence on performance. In certain cells, for example, for every 8.3° C. (15° F.) average annual temperature above 25° C. (77° F.), the life of the cell is reduced by approximately 50 percent. In other cells, for every 10° C. increase in temperature the reaction rate of undesired side-reactions doubles. Thus, an hour of operation at 35° C. is the same in terms of cell life as two hours of operation at 25° C. Methods described herein allow for optimization of the cell for operation at desired temperature or use conditions via a multiple electrolyte activation process during the initial manufacture of the electrochemical cell, and/or for refurbishment of the electrochemical cell if typical use, excessive use, or operation under extreme conditions caused degradation of the EEI and/or electrolyte over its lifetime. Such refurbishment may act in prolonging cell lifetime at a given temperature up to 200%. Various structures, either sacrificial or reusable structures such as fill tubes or sealing constructions, may be provided on or with the electrochemical cell itself to facilitate the methods.
Throughout the discussion below, use of the terms “about” and “approximately” are used to indicate engineering tolerances which would be well understood by a person of ordinary skill in the art for any particular application or embodiment. Further, while an order of the method steps is provided, this order is exemplary only; as will be recognized by those of skill in the art, the order of the method steps may be varied without impacting the overall efficacy of the method.
The present methods create a unique electrode-electrolyte interphase (EEI) to optimize performance of an electrochemical cell for specific conditions and/or to allow for refurbishment of a spent electrochemical cell. In some embodiments, the EEI is created by selecting a first electrolyte, introducing the first electrolyte into a cell, sealing the cell, and then activating the cell. Electrochemically activating the cell (i.e., charging to a specified voltage) causes selective components of the first electrolyte to decompose or otherwise react with the surface(s) of the cathode(s) and anode(s) of the cell. The seal of the electrochemical cell is then opened, and at least a portion of the remaining first electrolyte and any as-formed gases are extracted from the cell. In some examples, all or substantially all of the remaining first electrolyte and any as-formed gases are extracted. A second electrolyte having a different composition from the first electrolyte is then introduced into the cell. The second electrolyte is selected so that the unique EEI either optimizes the performance of the second electrolyte over a broader range of conditions or allows the second electrolyte to perform efficiently where passivation or other degradation of the electrode(s) may have occurred that would inhibit performance of other electrolyte compositions.
Container 210 houses a cell stack 215 (as shown in
Cathode layer 640 may be any type of cathode material known in the art. In some embodiments, cathode layer 640 may be selected from the following materials: LiCoO2, LiNiO2, LI(NixMnyCoz)O2, other lithium-manganese oxides, Li(NixCoyAlz)O2, lithium-ion phosphate, FeS2, V2O5, electrically conducting polymers, cathodes for non-lithium-based cell as will be known to those in the art, and/or a blend of these or other known materials.
Anode layer 650 may be any type of anode material known in the art. In some embodiments, anode layer 650 may be selected from the following materials: electrochemically active graphites such as meso-carbon micro bead (MCMB), hard carbon, other forms of natural or artificial graphite, graphitic carbon, amorphous carbons, graphene, silicon, alloys containing transition elements and/or Sn, Bi, Ge, etc., and active metals (i.e., lithium, sodium), metal oxides such as lithium titanium oxide, and lithium metal oxides/nitrides, tin-based alloys, silicon-based materials, materials for non-lithium-based cells as will be known to those in the art, and/or a blend of these or other known materials.
Separator layer 660 may be any type of separator known in the art, such as a gelatinous microporous membrane configured to block physical contact between cathode layer 640 and anode layer 650 to prevent short-circuiting of the electrodes while allowing the diffusion of ions through separator layer 660. In some embodiments, a porous polymer membrane such as Celgard® may act as separator layer 660.
In some embodiments, container 210 may be hermetically sealed so that container 210 is airtight to prevent the ingress of oxygen, moisture, and any external contaminants from entering into the interior of container 210 or loss of electrolyte from container 210. In other embodiments, electrochemical cell 200 and/or container 210 may include seals (not shown) that are not hermetic but are semi-hermetic so that the container is nearly airtight or airtight for known periods of time. In other embodiments, the seals may not be airtight but may be sufficient to contain the electrolyte within cell 200 and/or container 210 and prevent invasion of air, moisture, and/or contaminants into cell 200 and/or container 210 for a desired period of time.
In some embodiments, container 210 may include access for introducing container 210 with an electrolyte so that the remaining seals of container 210 may remain intact throughout the filling and extraction processes. In some embodiments, container 210 may include access such as a fill tube 220. Fill tube 220 may extend through at least one wall of container 210 to provide access to an interior of container 210 from the exterior environment. Fill tube 220 may be any size or shape to allow for the introduction and extraction of electrolyte and/or as-formed gases into and from the interior of container 210. Fill tube 220 may be made from any material that is capable of being associated with container 210 and is generally non-reactive to any electrolyte or other active component of electrochemical cell 200. Fill tube 220 may include various optional structures to allow for ease of introduction and extraction of electrolyte to electrochemical cell 200 and/or container 210, such as elastomeric ports that can accommodate and seal to multiple types of injection/extraction structures, a tapered nozzle 322 in the interior of container 210 to allow for rapid dispersion or extraction of an electrolyte throughout the interior of container 210, a porous portion (not shown) within interior of container 210 to allow for controlled dispersion or extraction of electrolyte to or from container 210, and/or interior channels (not shown) within container 210 to further control the dispersion or extraction of an electrolyte to or from container 210.
Thus, in an embodiment of the method that uses an access such as fill tube 220, first electrolyte step 110 includes associating a first electrolyte reservoir such as first electrolyte reservoir 310 containing a first electrolyte 300 shown in
In some examples, access to fill tube 220 may include the step of unsealing fill tube 220. For example, unsealing fill tube 220 may include puncturing or breaking a permanent seal, uncrimping an opening of fill tube 220, and/or opening a temporary seal by removing a cap or press-fitted portion. Those of skill in the art will recognize the type of seal used for fill tube 220 and will recognize how to create access to fill tube 220.
When an access such as fill tube 220 is not provided, first electrolyte step 110 may include opening container 210 using any method known in the art, such as puncturing or breaking a permanent seal, removing a wall or portion of a wall of container 210, or opening a temporary seal of container 210 by removing a cap or press-fitted portion. Those of skill in the art will recognize the type of seal used for container 210 and will recognize how to create access to container 210.
First electrolyte 300 may be selected from any type of electrolyte known in the art that can be introduced and extracted from an electrochemical cell, such as liquid, gel, gas (at ambient temperature and pressure) or solid electrolyte. Liquid electrolytes, either aqueous or non-aqueous, may be particularly suitable for use in the present method such as method 100 or method 150. Gel electrolytes may require heating to be able to perform the desired introduction and extraction steps of the present methods. Solid electrolytes may require a larger opening for introduction and extraction, such as a hinged casing with high-grade elastomeric seals and temporary fasteners or cutting open container 220 and re-sealing by welding or other methods known in the art, to allow for introduction and extraction into cell 200. Additionally, for gel and solid electrolyte processes, a primary (liquid, gas, gel, or solid) electrolyte may be added to perform the initial activation of the cell 200 and to form necessary interfacial layer(s) that will enable beneficial processes such as facilitating intimate contact with the secondary gel/solid electrolyte, or form a stable EEI that would otherwise limit the specific composition of the gel/solid electrolyte, and/or improve manufacturing processes such as wetting of the electrode. Solid electrolytes may be utilized as a composite within the electrodes themselves, requiring appropriate processing steps at their interfaces as would be known by those in the art.
First electrolyte 300 may be selected to have a composition that will produce the desired surface EEI on the electrodes, such as cathode EEI 642 and anode EEI 652 shown in
After filling electrochemical cell 200 with first electrolyte 300, access to the interior of container 210 can be sealed. For example, fill tube 220 may be crimped, welded, capped, or otherwise permanently or temporarily sealed. The seal may be hermetic, semi-hermetic, or not hermetic.
First electrolyte 300 may be provided in a specialized container (not shown) that may not be part of a stand-alone electrochemical cell. For example, the specialized container may be part of a bath in a manufacturing process that does not contain structures for ongoing electricity generation such as a cell stack, but does contain the structures capable of electrochemically activating first electrolyte 300 so that the desired surface EEI may be formed on the electrode(s) inserted into the specialized container. This specialized container may be reusable, such as in a manufacturing setting, so that the electrode(s) may be removed from the specialized container after the desired surface EEI has been formed and then transferred to another site, facility, or storage location for incorporation into a stand-alone electrochemical cell. Another electrode or electrodes may then be placed into the specialized container for EEI development. In this way, extraction of the first electrolyte 300 need not occur for each electrochemical cell in production.
The desired surface EEI is formed upon electrochemical activation of the electrochemical cell such as electrochemical cell 200. In methods 100 and 150, this initial electrochemical activation occurs in first activation step 120. Activation is considered herein to include all electrical, temperature, and physical handling steps performed during the final stages or near to the final stages of assembly of an electrochemical cell or in the refurbishment of an electrochemical cell, while electrochemical activation is the step in the process of activation of the electrochemical cell where a voltage or current is drawn or applied to the electrochemical cell 200. During a typical electrochemical activation process, the electrochemical cell 200 is subjected to both constant voltages and high and low currents (charge and discharge). Optionally, the electrochemical cell 200 may be subjected to temperature cycles in one or more additional, non-electrochemical activation step(s). The activation and electrochemical activation steps are well-known in the art, and any variations in temperature, voltage, duration, etc., to achieve desirable EEI characteristics through a reaction of an electrolyte with the electrode(s) will be discernable to those in the art.
The electrochemical activation of the cell in the present methods may include charging the electrochemical cell 200 to a first voltage cutoff at a predetermined temperature and time to trigger the electrochemical decomposition of first electrolyte 300. This decomposition may include various components of first electrolyte 300, such as salts, solvents, and additives. Any combination of the salts, solvents, and/or additives may be selected to produce a unique EEI with specific properties. For example, the unique EEI may be formed to optimize performance characteristics at high temperatures, so that a replacement electrolyte may function efficiently at lower operational temperatures as well as operative efficiently at high temperatures. In other examples, the EEI may be formed to optimize performance at high currents and/or voltages, large discharge depths, rapid charge/discharge cycling, to achieve extended storage shelf-life, and/or reduced self-discharge. In still other examples, the unique EEI may be formed to allow for refurbishment and efficient use at the end of the life cycle of the electrochemical cell with the original electrolyte, where a replacement electrolyte still efficiently accesses the electrodes using the EEI despite apparent passivation or degradations of the electrode(s) by the original electrolyte.
In some examples, the EEI may be similar to cathode EEI 642 and anode EEI 652 shown in
Once the desired EEI is formed, the remaining first electrolyte 301 is at least partially extracted from the electrochemical cell 210 in extraction step 130 as illustrated in
In some embodiments with liquid electrolytes or flowable gel electrolytes, to extract the remaining first electrolyte 301, which may be compositionally different from first electrolyte 300 due to the decomposition process and the possible presence of as-formed gas, remaining first electrolyte 301 is drawn away from cell stack 215, into tapered nozzle 322 in extraction direction 426, and into fill tube 220. One or more electrolytes may be composed of pressurized gas phases with or without conducting salts in which extraction/filling processes are controlled by appropriate equipment and hardware not specifically described here. A preliminary step of unsealing fill tube 220 or container 210 may first be performed. The unsealing of fill tube 220 or container 210 may be accomplished using any method discussed above with respect to unsealing any portion of electrochemical cell 200.
Once extraction begins, at least a portion of remaining first electrolyte 301, and in some examples, all or substantially all of remaining first electrolyte 301 flows through fill tube 220 in extraction flow direction 424. At least a portion of remaining first electrolyte 301 is then drawn into and collected in second reservoir 311 for reuse or other disposition. A portion of remaining electrolyte 301 may be allowed to remain for mixture with a second electrolyte such as second electrolyte 500 shown in
To optimize the performance of or to refurbish electrochemical cell 200, a second electrolyte, such as second electrolyte 500 shown in
Second electrolyte 500 may be selected to have a composition that interacts with the deposited EEI on the electrodes, such as cathode EEI 642 and anode EEI 652 shown in
Once the desired second electrolyte 500 is selected to match the desired properties provided by the unique EEI formed from the decomposition of first electrolyte 300, second electrolyte 500 is introduced into electrochemical cell 200 in second electrolyte step 140 as illustrated in
To complete this multi-electrolyte activation process, such as method 100, a second electrochemical activation step 160 of electrochemical cell 200 is performed. Second electrochemical activation step 160 is similar to first electrochemical activation step 120 discussed above. As will be recognized by those of skill in the art, the voltage, temperature, and duration of second electrochemical activation step 160 may differ from that of first electrochemical activation step 120 due to the different compositions of first electrolyte 300 and second electrolyte 500 as well as potentially desiring a different end result. For example, first electrochemical activation step 120 may be used to optimize a performance characteristic of electrochemical cell 200 by creating the unique EEI. As such, first electrochemical activation step 120 may be of a minimum acceptable duration so as to achieve sufficient build-up of the decomposition materials onto the electrodes. For second electrochemical activation step 160, however, the duration may be significantly shorter because the intention is not to create a unique EEI layer but simply to activate the electrochemical cell 200.
Electrochemical cell 200 with the unique EEI formed by the decomposition of first electrolyte 300 onto the electrodes may have optimized performance over the use of just first electrolyte 300 or second electrolyte 500. For example, first electrolyte 300 may have efficient performance for high temperatures, such as temperatures in excess of 45 degrees Celsius. However, first electrolyte 300 may have poor performance at lower temperatures, such as at room temperature and below. Second electrolyte 500 may have good performance at a wide range of typical use temperatures, such as −20 to 60 degrees Celsius, but poor performance with regard to voltage/temperature stability that is otherwise mitigated by the EEI formed by first electrolyte 300. By creating the EEI using the decomposition of first electrolyte 300, second electrolyte 500 can take on some of the performance properties of first electrolyte 300 and may have good performance beyond that of either electrolyte composition alone.
As will be recognized by those in the art, multiple iterations of method 100 or other exemplary embodiments of the present method may occur. For example, as shown in
Other devices and methods for introducing electrolytes into the electrochemical cell are contemplated herein. As illustrated in
As will be recognized by those in the art, the electrodes themselves have been optimized for a particular use, such as storage and/or operation at extreme temperatures and/or pressures, or extreme usage conditions such as rapid charge/discharge cycling and/or subjecting an electrochemical cell to large discharge depths, by providing the electrodes with a unique EEI. These unique electrodes and EEIs could have any of the characteristics discussed above with respect to electrode type, EEI type, the amount of coverage of the EEI only the electrode (i.e., complete coverage or patches of EEI formed on the electrode surface), and the thickness of the EEI on the electrode. As such, the unique EEI electrodes themselves may, in an initial use and/or refurbishment situation, be transferred from a first container to another container where the first container may or may not be part of a stand-alone electrochemical cell. Unique EE electrodes may also be provided separately from the rest of the structure of the end-use electrochemical cell. For example, the unique EEI electrodes may be manufactured in one facility or part of a facility and then provided to another facility or other part of a facility for incorporation into an electrochemical cell.
The methods and techniques discussed above may be used with any type of cell including dry cells, which are typically manufactured in tightly controlled environments, such as clean rooms with very low humidity (in some embodiments a dry room or dry box) and tight temperature controls. Therefore, it is anticipated that in many cases, even when the electrochemical cell is a dry cell, this method would be performed during the initial manufacture of an electrochemical cell such as electrochemical cell 200 for the multi-electrolyte activation/optimization of performance characteristics or that electrochemical cell 200 would be returned to a manufacturing site for refurbishment. However, in certain industries such as the oil and gas industry or military, the industries will have access to appropriate manufacturing spaces and skilled personnel to be able to perform these methods. In these cases, a kit with any special tools required to unseal electrochemical cell 200, appropriate electrolytes with or without reservoirs such as reservoir 310 or 510, parts to associate the electrolyte reservoirs to electrochemical cell 200, unique EEI electrodes, and/or instructions for how to perform the method may be provided, either with the initial purchase of the electrochemical cell or as a stand-alone purchase.
Experimental Results for High Temperature Electrochemical Cells
Various tests were performed using embodiments of a multi-step activation method according to the methods discussed herein, such as method 100. While discussed in terms of method 100, other similar methods or embodiments are equally applicable to this testing procedure. In this testing procedure, three groups of cells with a pouch construction, similar to the pouch shown in
For cells in Groups A and B, the first electrolyte for step 110, filling the cell with a first electrolyte, includes a combination of traditional Li-Ion battery electrolyte (containing LiPF6 salt dissolved in a mixture of carbonate-based solvents to form a good EEI layer) and ionic liquid-based electrolyte (to improve high-temperature stability) in a LiCoO2/graphite-based pouch cell with a capacity of 170 mAh were provided. Group C had a similar structure, but was filled with a PMP-based ionic liquid. A commercial polyethylene-based separator was used to separate the LCO (LiCoO2) based positive electrode and the graphite based negative electrode.
All cells were activated using a multi-stage activation procedure, shown in
The first electrolyte was then replaced with a second electrolyte that will operate in extreme temperatures and activated in a second stage in steps 850 to 880, similar to the methods discussed herein such as method 100. The first electrolyte was extracted along with any formed gases and a second electrolyte was introduced into the pouch. In the first group of cells, Group A, cells were opened by trimming on side of the pouch seal in a dry room (dew point −30° C. or better). The trimming allowed for release of gas (if any) that formed during the initial conditioning under vacuum, then refilled with standard Li-Ion battery electrolyte with a formulation of 1.2M LiPF6 EC/EMC (30/70), (EC—Ethylene Carbonate and EMC—Ethyl Methyl Carbonate). The pouch was then resealed to continue the activation process shown in
In the second group of cells, Group B, the cells, in a dry room (dew point −30° C. or better), Group B cells were opened by trimming the side of the pouch seal. The inside of the pouch was rinsed with 4 mL of EMC and vacuum dried. After vacuum drying, 0.7 mL of ionic liquid-based electrolyte was added to the pouch, and the cells were resealed under vacuum and the conditioning steps were continued.
In the third group of cells, Group C, the cells were trimmed on the side of the pouch seal in a dry room (dew point −30° C. or better). The trimming allowed for release of gas (if any) that formed during the initial conditioning under vacuum, then refilled with a PMP based ionic liquid. The pouch was then resealed to continue the activation process shown in
All groups of cells were cycled three more times at 30 mA for both charge and discharge to stabilize the cell capacity in stabilization step 850. Next, in self-discharge step 860, all cells were charged to 4.2V at 30 mA and rested for 72 h to measure the self-discharge voltage loss, and followed by a discharge at 30 mA to 3.0 V. On the final cycle, in resistance step 870, all cells were charged to 4.2 V at 30 mA and discharged to 3.0 V at 30 mA with 10%, 50%, and 100% depth-of-discharge (DOD) with 600 mA for 100 ms pulse to calculate cell resistance at different DOD. In a half-charge step 880, all cells were charged to 3.8 V at 30 mA and discharged to 1.5 mA. The Group C cells were swollen (showed gassing) after the conditioning process was completed and were removed from further testing.
Results
Various measures of the cells were taken during the testing procedure. For each group of cells, Groups A-C, a first charge voltage profile during the first charge from step 810 to 820 were taken and shown in
At soak step 830, the 50 degree Celsius soak potentials were measured. The Group A 50 degree Celsius soak potential is shown in
At stabilization step 850, the discharge capacity of the cells were measured for each of the groups. The Group A discharge capacity is shown in
The final stabilization voltage profiles of the cells were measured for each of the groups for the period after step 850. The Group A final stabilization voltage profiles are shown in
At self-discharge step 860, the self-discharge evaluation potentials of the cells were measured for each of the groups. The Group A self-discharge evaluation potential is shown in
High Temperature Storage Test
Because swelling of cells is a known issue during storage of cells at high temperatures, three cells from each group were charged to 4.2 V (100% state-of-charge of the cell) at 30 mA, then stored at 85° C. for one week. After one week of storage at 85° C., the cells were allowed to return to room temperature, and the cell thickness was measured using the parallel plate measurement method. The results are summarized in the table shown in
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated to explain the nature of the subject matter, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. The steps of the methods described above may be performed in any order unless the order is restricted in the discussion. Any element of any embodiment may be used in any other embodiment and/or substituted for an element of any other embodiment unless specifically restricted in the discussion.
This application claims priority to Provisional Patent Application 62/952,686, titled “System and Method for Multi-Electrolyte Activation and Refurbishment of Electrochemical Cells”, filed on Dec. 23, 2019, the contents of which are hereby incorporated by reference in their entirety.
The United States Government has rights in this invention pursuant to the employer-employee relationship of the Government to at least one inventor.
| Number | Date | Country | |
|---|---|---|---|
| 62952686 | Dec 2019 | US |
