Patent Application
20230411585
Not Applicable
Not Applicable
The present disclosure relates generally to manufacturing energy storage devices such as Li-ion batteries and, more particularly, to dry processes for the manufacture of electrodes for energy storage devices.
As demand for inexpensive energy storage devices increases, various methods have been proposed for manufacturing electrodes. Among these, there exist so-called “dry” processes by which a free-standing electrode film may be manufactured while avoiding the expense and drying time associated with the solvents and aqueous solutions that are typically used in slurry coating and extrusion processes. After a free-standing electrode film is produced, it is laminated to a current collector in order to produce an electrode. While there have been some attempts at devising a continuous process that both produces a free-standing electrode film and laminates the free-standing electrode film to a current collector (see, e.g., German Patent Application Pub. No. DE 10 2017 208 220), the success of such processes has been limited, in part due to the difficulty of producing a uniform electrode film and handling the free-standing electrode film without breaking it. The challenges are especially significant for thinner electrode films or for electrode films that are made to be less flexible from materials such as battery active materials, including, but not limited to, lithium nickel manganese cobalt oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium iron phosphate (LFP), graphite, and silicon, which can be more difficult to work with than activated carbon, for example.
The present disclosure contemplates various apparatuses and methods, as well as related products, for overcoming the above drawbacks accompanying the related art. One aspect of the embodiments of the present disclosure is an apparatus for manufacturing an electrode for an energy storage device. The apparatus may comprise at least one laminator for simultaneously laminating two free-standing electrode films on opposite sides of a current collector and a pair of mill lines operable to produce, respectively, the two free-standing electrode films and to feed the two free-standing electrode films simultaneously to the laminator. Each of the mill lines may comprise at least one first press including working rolls arranged horizontally for pressing a powder mixture into a respective one of the free-standing electrode films and at least one second press including working rolls (typically arranged vertically) for reducing the thickness of the respective free-standing electrode film.
The apparatus may comprise a mill line expansion module. The mill line expansion module may be insertable into a mill line of the pair of mill lines and may comprise at least one additional second press including working rolls (typically arranged vertically) for reducing the thickness of the respective free-standing electrode film. In general, the number of presses may be directly related to the final electrode film thickness, porosity, and density and the corresponding film mechanical strength such as breakage elongation and tensile strength, as well as the speed of the mill lines. By employing a modular system rather than having a fixed number of presses, the apparatus can tailor these parameters for various material types with different electrode specifications.
Each of the mill lines may comprise one or more conveyors arranged to support the respective free-standing electrode film as it is fed from the at least one second press of the mill line to the laminator. The one or more conveyors may be arranged to support the respective free-standing electrode film as it is fed from a first of the at least one second press to a second of the at least one second press of the mill line. A speed of the one or more conveyors between the at least one second press of the mill line and the laminator may be controlled to be different from a speed of the one or more conveyors between the first of the at least one second press and the second of the at least one second press of the mill line. The one or more conveyors may be arranged to support the respective free-standing electrode film as it is fed from the at least one first press to the at least one second press of the mill line. The speeds of the conveyor(s) between each stage, including between the first press and the first of the second press(es), between any adjacent second press(es), and between the second press(es) and the laminator, may be controlled to be different. Each of the mill lines may comprise one or more tension sensors arranged to measure a tension of the free-standing electrode film. A speed of the one or more conveyors of the mill line and/or a speed of the working rolls of the at least one second press of the mill line may be controlled based on the measured tension, e.g., to prevent film breakage. The one or more conveyors may comprise at least one vacuum conveyor.
Another aspect of the embodiments of the present disclosure is a method of manufacturing an electrode for an energy storage device. The method may comprise providing the above apparatus, preparing a first powder mixture including an electrode active material and a fibrillizable binder, fibrillizing the fibrillizable binder in the first powder mixture by subjecting the first powder mixture to a shear force, pressing the first powder mixture into a first free-standing electrode film using the at least one first press of a first mill line of the pair of mill lines, reducing the thickness of the first free-standing electrode film using the at least one second press of the first mill line, and laminating the first free-standing electrode film on a first side of a current collector using the at least one laminator.
The method may comprise preparing a second powder mixture including an electrode active material and a fibrillizable binder, fibrillizing the fibrillizable binder in the second powder mixture by subjecting the second powder mixture to a shear force, pressing the second powder mixture into a second free-standing electrode film using the at least one first press of a second mill line of the pair of mill lines, reducing the thickness of the second free-standing electrode film using the at least one second press of the second mill line, and, simultaneously with said laminating the first free-standing electrode film on the first side of the current collector, laminating the second free-standing electrode film on a second side of the current collector opposite the first side using the at least one laminator.
Another aspect of the embodiments of the present disclosure is a method of manufacturing an electrode for an energy storage device. The method may comprise preparing a first powder mixture including an electrode active material and a fibrillizable binder, fibrillizing the fibrillizable binder in the first powder mixture by subjecting the first powder mixture to a shear force, preparing a second powder mixture including an electrode active material and a fibrillizable binder, fibrillizing the fibrillizable binder in the second powder mixture by subjecting the second powder mixture to a shear force, and simultaneously producing a first free-standing electrode film from the first powder mixture and a second free-standing electrode film from the second powder mixture using a pair of mill lines, each of the mill lines comprising at least one first press including working rolls arranged horizontally for pressing the respective powder mixture into the respective free-standing electrode film and at least one second press including working rolls (typically arranged vertically) for reducing the thickness of the respective free-standing electrode film. The method may further comprise, continuously with said producing the first and second free-standing electrode films, feeding the first and second free-standing electrode films from the respective mill lines to a laminator and laminating the first and second free-standing electrode films on opposite sides of a current collector.
The method may comprise supporting the first free-standing electrode film using one or more conveyors as the first free-standing electrode film is fed from the respective mill line to the laminator. The method may comprise supporting the first free-standing electrode film using the one or more conveyors as the first free-standing electrode film is fed from a first of the at least one second press to a second of the at least one second press of the respective mill line. The method may comprise controlling a speed of the one or more conveyors between the respective mill line and the laminator to be different from a speed of the one or more conveyors between the first of the at least one first press and the second of the at least one first press of the respective mill line. The method may comprise supporting the first free-standing electrode film using the one or more conveyors as the first free-standing electrode film is fed from the at least one first press to the at least one second press of the respective mill line. The method may comprise controlling the speeds of the conveyor(s) to be different between each stage, including between the first press and the first of the second press(es), between any adjacent second press(es), and between the second press(es) and the laminator. The method may comprise measuring a tension of the first free-standing electrode film and controlling a speed of the one or more conveyors and/or a speed of the working rolls of the at least one second press based on the measured tension, e.g., to prevent film breakage. The one or more conveyors may comprise at least one vacuum conveyor.
Another aspect of the embodiments of the present disclosure is a free-standing electrode film. The free-standing electrode film may comprise an electrode active material and a fibrillizable binder. A machine direction elongation percentage of the free-standing electrode film may be less than 4%. The machine direction elongation percentage of the free-standing electrode film may be less than 2%. A machine direction tensile strength of the free-standing electrode film may be greater than 450 kPa. The porosity of the free-standing electrode film may be less than 32%.
These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:
The present disclosure encompasses various embodiments of apparatuses for manufacturing electrodes for energy storage devices as well as manufacturing methods and intermediate and final products thereof. The detailed description set forth below in connection with the appended drawings is intended as a description of several currently contemplated embodiments and is not intended to represent the only form in which the disclosed invention may be developed or utilized. The description sets forth the functions and features in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the present disclosure. It is further understood that the use of relational terms such as first and second and the like are used solely to distinguish one from another entity without necessarily requiring or implying any actual such relationship or order between such entities.
Depending on the particular application of the energy storage device to be manufactured, the dry powder mixtures 12a, 12b used to produce the free-standing electrode films 10a, 10b may have various formulations and may be produced according to various methods. Some exemplary dry powder formulations and methods that may be used to produce the dry powder mixtures 12a, 12b are described in the inventor's own patents and patent applications, including U.S. Pat. No. 10,069,131, entitled “Electrode for Energy Storage Devices and Method of Making Same,” U.S. Patent Application Pub. No. 2020/0388822, entitled “Dry Electrode Manufacture by Temperature Activation Method,” U.S. Patent Application Pub. No. 2022/0077453, entitled “Dry Electrode Manufacture with Lubricated Active Material Mixture,” U.S. patent application Ser. No. 17/097,200, entitled “Dry Electrode Manufacture with Composite Binder,” and U.S. patent application Ser. No. 17/492,458, entitled “Dry Electrode Manufacture for Solid State Energy Storage Devices,” the entire disclosure of each of which is wholly incorporated by reference herein. Typically, since the first and second free-standing electrode films 10a, 10b will be disposed by the apparatus 100 on the same current collector 20, both dry powder mixtures 12a, 12b will be formulated and produced in the same way (and thus in practice may be divided from the same production batch, for example).
Each of the mill lines 120a, 120b may comprise at least one first press 122a, 122b for pressing one of the powder mixtures 12a, 12b into a respective free-standing electrode film 10a, Referring to the mill line 120a by way of example (equivalent reference numbers using the letter “b” instead of “a” in the case of the mill line 120b), the first press 122a may include working rolls 123a-1, 123a-2 arranged horizontally as shown, such that the powder mixture 12a may be poured on top of the working rolls 123a-1, 123a-2 (from a powder feed conveyor 13a, for example) and emerge from the bottom thereof in the form of a continuous film having been subjected to pressure and heat by the working rolls 123a-1, 123a-2. To this end, the working rolls 123a-1, 123a-2 of the first press 122a may have elevated surface temperatures (e.g., greater than 70° C.). Advantageously, the working rolls 123a-1, 123a-2 may be controlled to rotate at the same speed as each other, with the gap between the working rolls 123a-1, 123a-2 being freely adjustable to affect the film density and porosity as desired for the particular material and application. In this regard, it is noted that it may be unnecessary for the first press 122a to produce a shear effect by the operation of working rolls 123a-1, 123a-2 having different speeds, especially in a case where the powder mixture 12a has been produced by one of the exemplary methodologies referred to above in which the powder mixture 12a has already been subjected to a shear force using a jet mill, for example.
Each of the mill lines 120a, 120b may further comprise at least one second press 124a, 124b for reducing the thickness of the respective free-standing electrode film 10a, 10b. Referring again to the mill line 120a by way of example, the second press 124a may include working rolls 125a-1, 125a-2 that are typically (though not necessarily) arranged vertically as shown. Like the working rolls 123a-1, 123a-2 of the first press 122a, the working rolls 125a-1, 125a-2 of the second press 124a may have elevated surface temperatures (e.g., greater than 70° C.) and may be controlled to rotate at the same speed as each other, with the gap between the working rolls 125a-1, 125a-2 being freely adjustable as desired. While only a single second press 124a is shown in
As newer energy storage device applications begin to require electrodes made from thinner free-standing electrode films 10a, 10b, and as the possibilities for active materials grow to encompass materials that produce less flexible and more breakable free-standing electrode films 10a, 10b, conventional roll-to-roll processing apparatuses and methods may be inadequate for handling the free-standing electrode films 10a, 10b without breakage. Therefore, in order to better support each free-standing electrode film 10a, 10b as it passes through the respective mill line 120a, 120b toward the laminator 110 (after which the free-standing electrode film 10a, 10b will be adequately supported by the sturdier current collector 20 and will no longer be free-standing), it is contemplated that each mill line 120a, 120b may comprise one or more conveyors 126a, 126b such as vacuum conveyors, for example. Referring to the mill line 120a by way of example, the one or more conveyors 126a may be arranged to support the free-standing electrode film 10a at any of various positions including, for example, i) as the free-standing electrode film 10a is fed from the second press(es) 124a of the mill line 120a to the laminator 110, ii) as the free-standing electrode film 10a is fed from a first of the second press(es) 124a to a second of the second press(es) 124a, and/or iii) as the free-standing electrode film 10a is fed from the first press(es) 122a to the second press(es) 124a. The speed of each conveyor 126a may be controlled in accordance with the thickness and tension of the free-standing electrode film 10a at each particular position, which may be determined by the arrangement of the presses 122a, 124a and roller speeds thereof, as well as that of the downstream laminator 110. For example, the speed(s) of the conveyor(s) 126a between the second press(es) 124a and the laminator 110 may be controlled to be different from the speed(s) of the conveyor(s) between successive second press(es) 124a, which may in turn be different from the speed(s) of the conveyor(s) between the first press(es) 122a and the second press(es) 124a. In practice, the speeds of the conveyor(s) 126a may be controlled in a cascading fashion, with a final laminator speed 110 determining the speeds at each upstream position of each mill line 120a, 120b. As feedback to the control process, each mill line 120a, 120b may comprise one or more tension sensors 128a, 128b arranged to measure a tension on the free-standing electrode film 10a, 10b. Load cells or other proximity sensors may be employed to maintain the optimum tension control by adjusting the conveyor and working roll rotation speeds. The variable speed(s) and/or speed ratio(s) of the one or more conveyor(s) 126a, 126b may be controlled so that speed(s) between presses are appropriately matched based on the measured tension(s) using any of various algorithms including machine learning models, allowing the lamination speed to remain constant and preventing rupture of the films 10a, 10b.
Like each second press 124a, 124b of the respective mill lines 120a of the base apparatus 100, each additional second press 154a introduced by a mill line expansion module 150 may include working rolls 155a-1, 155a-2 that are typically (though not necessarily) arranged vertically as shown. The working rolls 155a-1, 155a-2 of each additional second press 154a may have elevated surface temperatures (e.g., greater than 70° C.) and may be controlled to rotate at the same speed as each other, with the gap between the working rolls 155a-1, 155a-2 being freely adjustable as desired. It is contemplated that the mill line expansion module 150 may further include one or more additional conveyors 156a that are insertable between conveyors 126a of the mill line 120a as shown. The mill line expansion module 150 may further include one or more additional tension sensors 158a that are arranged to measure a tension on the free-standing electrode film 10a as it passes through (e.g., before or after) the additional second press(es) 154a of the mill line expansion module 150. The additional conveyor(s) 156a and additional tension sensor(s) 158a may be connected to the same speed control system as the conveyor(s) 126a and tension sensor(s) 128a of the base apparatus 100. It is noted that the mill line expansion module 150 may be symmetrically designed for insertion in the mill line 120b rather than the mill line 120a as illustrated (and equivalent reference numbers using the letter “b” instead of “a” may be referred to in this case, though not separately illustrated).
By virtue of the mill line expansion module 150, the same apparatus 100 may be readily customizable for different production runs having different specifications for the energy storage device to be produced. A manufacturer of energy storage devices that are made using relatively thick free-standing electrode films 10a, 10b may use only the base apparatus 100 with no mill line expansion modules 150 or with only a single mill line expansion module 150 in each mill line 120a, 120b, while a manufacturer who needs to produce thinner free-standing electrode films 10a, may insert several mill line expansion modules 150 (or, in some cases, mill line expansion modules 150 having a greater number of additional second presses 154a, 154b, though a standardized mill line expansion module 150 may be preferable). The same apparatus 100 can satisfy the needs of both manufacturers, allowing for the efficient production and use of the apparatus 100 and mill line expansion modules 150. Without the modular design, it would be necessary either i) to market and produce a variety of different size apparatuses 100 or to custom-build the apparatus 100 for each manufacturer (with associated inefficiencies and costs in either case) or ii) to produce only the largest possible apparatus 100 with the highest possible number of second presses 124a, 124b that might be used. In the latter case, the apparatus 100 may become unreasonably expensive for a manufacturer who does not need to reduce the thickness of the free-standing electrode film 10a, 10b so much, both in terms of the purchase price but also in terms of maintenance and required personnel to oversee and run such a large apparatus 100. Moreover, any unused second presses 124a, 124b in a given run increase the risk of damaging the free-standing electrode film 10a, 10b as it is en route to the laminator 110, decreasing the yield of the run and making a large number of unused second presses 124a, 124b a liability for the manufacturer.
Along the same lines, a manufacturer who produces a variety of different products is better served by the modular apparatus 100, which may allow the manufacturer to increase or decrease the number of presses as need by attaching or detaching mill line expansion modules 150. The apparatus 100 may be used for some runs with several mill line expansion modules 150 and for other runs with few or none, decreasing the associated costs of these runs in terms of personnel and yield. As another possibility, it is contemplated that a mill line expansion module 150 may be used as a replacement in the event that the press(es) 154a, 154b of another mill line expansion module 150 need repair. Rather than shut down the entire manufacturing line pending the repair of the damaged press stations, the mill line expansion module 150 where the problem is occurring can simply be swapped for a fresh mill line expansion module 150. In this way, the manufacturing process can continue after only a moment's delay. The damaged mill line expansion module 150 can be repaired, without significantly interrupting production, even as the manufacturing process is ongoing.
The operational flow of
In particular, referring back to
Exemplary data of free-standing electrode films 10a, 10b made from three different active materials is provided in Table 1, below.
To produce each film group to the specified thickness (“Film Group” column), the disclosed apparatus 100 may be equipped with a suitable number of presses (“Number of Presses” column). In this regard, the number of presses shown in Table 1 (ranging from 1 to 15 for this data) should be understood to refer to all presses in a given mill line 120a, including both first press(es) 122a and second press(es) 124a, as well as any additional second press(es) 154a added using one or more mill line expansion modules 150. For example, the 250 μm NCM cathode film group (Number of Presses=1) may be produced using an apparatus 100 having a single first press 122a and no second press 124a in the mill line 120a used to produce the film, whereas the 65 μm NCM cathode film group (Number of Presses=15) may be produced with the same apparatus 100 having a single first press 122a in the mill line 120a but with fourteen additional second press(es) 154a added by mill line expansion modules 150. Table 1 shows an average thickness (“Avg. Thickness” column) that is exemplary of actual measured thicknesses corresponding to each film group in practice.
The last five columns of Table 1 show exemplary data of such films, where it can be seen that the tensile strength and film density of the film increases for thinner films and varies for different materials, while the elongation percentage (maximum machine direction elongation before breakage) and film porosity decreases for thinner films and likewise varies from material to material. The elongation percentage may be determined by a pull test (where the machine direction may refer to a draw direction in which the film is elongated by operation of the working rolls). An exemplary pull test may measure the distance pulled before breakage of a 2.5 cm wide by 10 cm long (machine direction) strip of film at an initial tension of 5 gf, for example. In particular, it is noted that the NCM cathode and graphite anode films are more difficult to work with than activated carbon films, owing to their being significantly less flexible (and thus having lower elongation percentages). As can be seen, the difficulty becomes even more pronounced for thinner films. By virtue of the apparatus 100 and associated processes described herein, it is contemplated that a wide variety of free-standing electrode films 10a, 10b can be successfully and efficiently produced on the same apparatus 100. For example, free-standing electrode films 10a, may be made of various materials including NCM, graphite, or activated carbon and may have thicknesses ranging from upwards of 300 μm down to as little as 50 μm or thinner. For each run of the apparatus 100, the mill lines 120a, 120b may be outfitted accordingly for the desired thickness or other parameters, expanded as needed by inserting mill line expansion modules 150 to increase the number of thickness-reducing presses. Moreover, owing to the innovative design of the apparatus 100, preferably including the conveyor(s) 126a, 126b, 156a, 156b to support the fragile films 10a, 10b as they pass through the mill lines 120a, 120b prior to being laminated on the current collector 20, it is contemplated that the resulting free-standing electrode films 10a, 10b may have tensile strengths ranging from 40 kPa up to greater than 100 kPa, greater than 450 kPa or even greater than 600 kPa (in the case of NCM or graphite) or, for very thin graphite anode films greater than 1100 kPa. At the same time, the machine direction elongation percentage may range from 10% down to less than 4% or even less than 2%, sometimes being as low as 0.50% or even 0.20% (in the case of NCM or graphite). The efficient handling of such fragile free-standing electrode films 10a, 10b would not be achievable without the disclosed innovations of the apparatus 100 and associated processes.
In general, it is contemplated that free-standing films having tensile strength of higher than 100 kPa and elongation percentage of less than 10% along the machine direction may require unique tension control designs to achieve high speed production processes. The use of the contemplated conveyors 126a, 126b, 156a, 156b combined with strategically placed sensors 128a, 128b (sometimes using multiple measurement methods) along the free-standing film axis may provide the necessary control to handle sensitive battery active material electrode films 10a, 10b. The difficulty in producing dry battery electrode in a free-standing film comes from the inherent brittle nature of the active materials that make conventional web handling methods impossible. By using conveyors 126a, 126b, 156a, 156b to support and transport the free-standing electrode film 10a, 10b through each press station in an automated self-threading process, the disclosed apparatus 100 and methods may overcome these difficulties.
Advantageously, the multiple press design of the apparatus 100 may allow for greater flexibility in tailoring the final electrode properties such as thickness uniformity, density, and porosity compared to other dry process electrodes produced with or without free-standing films. As shown in Table 1 above, by way of example, the film density may be selected as desired (e.g., between 3.02 g/cc and 3.40 g/cc for an NCM cathode or between 1.21 g/cc and 1.71 g/cc for a graphite anode) and likewise the film porosity may be selected as desired (e.g., between 25.9% and 34.2% for an NCM cathode or between 23.5% and 46.0% for a graphite anode), with low porosities (e.g., less than 32%) being achievable owing to the efficient handling of fragile free-standing electrode films 10a, 10b using the apparatus 100. In general, dry battery electrode technology requires the ability to control the loading, porosity, and uniformity of the active material layer. Other dry battery electrode processing techniques are not capable of precise tailored control of these parameters. For example, a dry spray or dry deposition electrode process that does not produce a free-standing film may be limited in the ability to control the thickness uniformity as the powder is sitting on top of the current collector and is unable to flow in multiple axes during the press. Additionally, the density and porosity may be limited by the amount of powder that can be applied to the current collector prior to pressing and the limitation of the pressing force that can be used without damaging the current collector. The disclosed innovations, by using multiple pressing stations working in tandem to produce free-standing electrode films 10a, 10b for both sides of the current collector 20 simultaneously can address all these requirements. Furthermore, having the system's thickness-reducing press stations in a modular configuration (employing a freely insertable mill line expansion module 150), rather than a fixed number of presses, allows for customization based on different material types such as anode materials or custom cathode materials.
In the above examples, it is described how the apparatus 100 may be used to produce a double-sided electrode by simultaneously running both mill lines 120a, 120b and laminating two free-standing electrode films 10a, 10b on opposite sides of a current collector 20. However, the processes described herein are not intended to be limited to the use of the apparatus 100 in this way. For example, in order to produce a single-sided electrode, a single mill line 120a of the apparatus 100 may be run, with the laminator 110 laminating only a single free-standing electrode film 10a on the current collector 20. It should also be recognized that any of the working rolls 112-1, 112-2 of the laminator 110, the working rolls 123a-1, 123a-2, 125a-1, 125a-2 of the mill line 120a, the working rolls 155a-1, 155a-2 of the mill line expansion module 150, and any corresponding working rolls provided in relation to the mill line 120b may be supported by one or more backing rolls such as a 4HI, 6HI, or cluster roll configuration.
The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.
