SCALABLE PRODUCTION OF AMORPHOUS SILICON ANODES FOR BATTERY CELLS

Abstract

A method of manufacturing an anode electrode for a battery cell comprises feeding a roughened anode current collector from a roll-to-roll chamber to a magnetron sputtering chamber; passing the roughened anode current collector around a roller in the magnetron sputtering chamber; using T sputtering targets circumferentially arranged around a portion of the roller, sputtering an amorphous silicon layer onto the roughened anode current collector to form an anode electrode, where T is an integer greater than one; and receiving the anode electrode from the magnetron sputtering chamber in the roll-to-roll chamber.

Description

INTRODUCTION

[0001] The information contained in this section is intended to provide a general context for the disclosure. Work by the inventors identified herein, to the extent described in this section, as well as aspects of the description that may not be prior art at the time of filing, are neither expressly nor impliedly admitted as prior art to the present disclosure.

[0002] The present disclosure relates to battery cells and, more particularly, to anode electrodes and methods of making anode electrodes for battery cells.

[0003] Electric vehicles (EVs), such as battery electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, comprise one or more electric machines and a battery system with one or more battery cells, modules, and / or packs. A power management system is used to control the charging and / or discharging of the battery system during charging and / or driving.

[0004] Battery cells comprise cathode electrodes, anode electrodes, and separators. The cathode electrodes comprise a cathode active material layer disposed on a cathode current collector. The anode electrodes comprise an anode active material layer disposed on an anode current collector. SUMMARY

[0005] A method of manufacturing an anode electrode for a battery cell comprises feeding a roughened anode current collector from a roll-to-roll chamber to a magnetron sputtering chamber; passing the roughened anode current collector around a roller in the magnetron sputtering chamber; using T sputtering targets circumferentially arranged around a portion of the roller, sputtering an amorphous silicon layer onto the roughened anode current collector to form an anode electrode, where T is an integer greater than one; and receiving the anode electrode from the magnetron sputtering chamber in the roll-to-roll chamber.

[0006] In other cases, the roughened anode current collector is made of a material selected from a group consisting of copper, stainless steel (SS), nickel (Ni), titanium (Ti), and tin (Sb). The roughened anode current collector has a roughness (Rz) in a range of 0.1 µm to 12 µm. The thickness of the roughened anode current collector is in a range of 0.1 µm to 40 µm. The thickness of the amorphous silicon layer is in a range of 0.1 µm to 20 µm.

[0007] In other features, the amorphous silicon layer comprises a plurality of silicon pillars. The diameter of the plurality of silicon pillars ranges from 0.1 µm to 15 µm. The average areal capacity of the anode electrode ranges from 4 to 30 mAh / cm 2 .

[0008] Other features include the DC bias voltage of the magnetron sputtering chamber ranging from 100 V to 1000 V. The cathode power of the magnetron sputtering chamber ranging from 0.5 kW to 30 kW.

[0009] A battery cell comprises A anode electrodes, each of the A anode electrodes comprising a roughened anode current collector. An anode active material layer comprises an amorphous silicon layer deposited by physical vapor deposition (PVD) on the roughened anode current collector C, wherein the cathode electrodes comprise a cathode current collector and a cathode active material layer on the cathode current collector. The battery cell comprises S separators, where A, C, and S are integers greater than one.

[0010] In other features, the roughened anode current collector is made of a material selected from a group consisting of copper, stainless steel (SS), nickel (Ni), titanium (Ti), and tin (Sb). The roughened anode current collector has a roughness (Rz) in a range of 0.1 µm to 12 µm. The thickness of the roughened anode current collector is in a range of 0.1 µm to 40 µm. The thickness of the amorphous silicon layer on the roughened anode current collector is in a range of 0.1 µm to 20 µm. The amorphous silicon layer includes a plurality of silicon pillars.

[0011] Other features include a diameter of the plurality of silicon columns ranging from 0.1 µm to 15 µm. An average areal capacity ranges from 4 to 30 mAh / cm 2 .

[0012] A system for manufacturing an anode electrode for a battery cell includes a roll-to-roll chamber and a magnetron chamber having a roll and T sputtering targets arranged circumferentially around a portion of the roll, where T is an integer greater than one. The roll-to-roll chamber delivers a roughened anode current collector to the magnetron sputtering chamber. The roughened anode current collector is wrapped around the roll in the magnetron sputtering chamber. The T sputtering targets sputter an amorphous silicon layer onto the roughened anode current collector to form an anode electrode. The anode electrode is wrapped from the magnetron sputtering chamber into the roll-to-roll chamber.

[0013] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are provided for purposes of illustration only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 is a side cross-sectional view of an example of a battery cell having A anode electrodes, C cathode electrodes, and S separators according to the present disclosure; Fig. 2A is a side cross-sectional view of an example of a roughened current collector and an amorphous silicon layer deposited on the current collector by PVD, according to the present disclosure; Fig. 2B is a top view of an example of a roughened current collector and an amorphous silicon layer deposited on the current collector by PVD, according to the present disclosure; Fig. 3 is a functional block diagram of an example of a magnetron for depositing amorphous silicon onto a roughened current collector; Fig. 4 is a functional block diagram of an example of a magnetron for depositing amorphous silicon using multiple targets onto a roughened current collector in a roll-to-roll process according to the present disclosure; Fig. 5A and Fig. 5B illustrates an example of the anode electrode during charging and discharging according to the present disclosure; Fig. 6 is a side cross-sectional view of an example of a battery cell having the liquid electrolyte anode electrode according to the present disclosure; Fig. 7 is a side cross-sectional view of an example of a battery cell having the solid electrolyte anode electrode according to the present disclosure; Fig. 8 are examples of scanning electron micrographs of top and side views of the anode electrode according to the present disclosure; Fig. 9A and Fig. 9B are examples of graphs of X-ray diffraction (XRD) profiles and Raman spectra of the anode electrodes according to the present disclosure; and Fig. 10A and Fig. 10B are examples of graphs illustrating capacity and percentage of capacity retention versus cycling for the anode electrodes according to the present disclosure.

[0015] Reference symbols may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0016] Although the battery cells according to the present disclosure are shown in the context of electric vehicles, the battery cells may be used in stationary applications and / or other applications.

[0017] Silicon is a promising candidate as an anode active material because it contains several lithium ions (Li + ) diffusion paths and a high theoretical capacity. The development of high-performance sheet-shaped silicon anodes is important for the construction of practical lithium-ion batteries. Generally, the sheet-shaped silicon anode is fabricated using a wet coating process. However, the delivered performance of the anode electrode and its cycling stability still need to be improved.

[0018] The present disclosure relates to a method for manufacturing an anode electrode comprising an amorphous silicon anode layer (e.g., comprising silicon pillars) deposited on a roughened copper current collector. The anode electrode may be manufactured in a scalable roll-to-roll manufacturing process.

[0019] In conventional wet coating processes, an anode active material, a conductive additive, a binder, and a solvent are mixed into a mixture. The mixture is poured onto an anode current collector, and the solvent is then removed through a drying step. The solvent is environmentally harmful, and the drying phase increases the process's environmental footprint.

[0020] The method for fabricating the anode electrode according to the present disclosure is by magnetron sputtering. This approach eliminates the use of the binder, conductive additive, and solvent, simplifying the silicon anode fabrication process while increasing energy density. Furthermore, the amorphous silicon layer includes damaged surfaces. The damaged surfaces allow for more contact interfaces with the electrolyte to increase Li ion conduction paths and contribute to stress relief during the volume change of the silicon during cycling.

[0021] With reference now to Fig. 1, a battery cell 10 includes C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a predetermined sequence in a battery cell stack 12, where C, S, and A are integers greater than zero. The battery cell stack 12 is arranged in a housing 50. The C cathode electrodes 20-1, 20-2, ..., and 20-C include cathode active material layers 24 arranged on one or both sides of a cathode current collector 26. The A anode electrodes 40-1, 40-2, ..., and 40-A include anode active material layers 42 arranged on an anode current collector 46. In some examples, the A anode electrodes 40 and the C cathode electrodes 20 exchange lithium ions during charging / discharging.

[0022] In some examples, the anode active material layer 42 comprises a silicon layer deposited by PVD on the anode current collector 46. The anode current collector 46 comprises a roughened current collector. In some examples, the cathode active material layers 24 comprise coatings with one or more active materials, one or more conductive additives, and / or one or more binders applied (cast or laminated) to the current collectors.

[0023] In some examples, the cathode current collector 26 comprises metal foil, metal mesh, perforated metal, three-dimensional (3D) metal foam, and / or expanded metal. In some examples, the cathode current collectors are formed from one or more materials selected from a group consisting of stainless steel, brass, bronze, zinc, and aluminum. The outer tabs 28 and 48 are connected to the current collectors of the cathode electrodes and anode electrodes, respectively, and may be disposed on the same or different sides of the battery cell stack 12. The outer tabs 28 and 48 are connected to the terminals of the battery cells.

[0024] In some examples, the battery cell 10 uses a liquid electrolyte 52. In other examples, a solid electrolyte, a gel electrolyte, and / or a liquid electrolyte is used.

[0025] With reference now to Fig. 2A and Fig. 2B, one of the A anode electrodes 40 is shown in further detail. In Fig. 2A, one of the anode electrodes 40 includes the anode current collector 46 and the anode active material layer 42. In some examples, the anode current collector 46 includes roughened surfaces 47 on its opposite sides. The anode active material layer 42 includes an amorphous silicon layer 60 deposited by physical vapor deposition (PVD). The Si morphology depends on the DC bias voltage and / or the performance of the silicon cathode during the roll-to-roll manufacturing process.

[0026] At a DC voltage of 100 to 500 V (e.g., 350-500 V) and / or a cathode power of 0.5 to 12 kW (e.g., 10 kW), the silicon is evenly and gently deposited on the roughened current collector, forming silicon columns with convex, spherical surfaces. In some examples, the height of the amorphous silicon layer on the roughened anode current collector (e.g., H S1 ≈ H S2 ≈ H Sn ) in a range from 0.1 µm to 20 µm.

[0027] In some examples, a diameter of the silicon columns (e.g. D S1 = D S2 = D Sn ) in a range of 0.1 µm to 15 µm. In some examples, the average areal capacity is in a range of 4 to 30 mAh / cm 2 (e.g. 10 to 20 mAh / cm 2 for double-sided plates).

[0028] In some examples, the roughened anode current collector includes a roughened surface to enable close interfaces with the amorphous silicon layer. In some examples, the roughened anode current collector has a roughness (Rz) in a range of 0.1 µm to 12 µm (e.g., 8 µm). In some examples, the thickness of the roughened anode current collector (e.g., H C1 , H C2 , H Cn ) in a range of 0.1 µm to 40 µm. In some examples, the roughened anode current collector is made of a material selected from the group consisting of copper, stainless steel, nickel (Ni), titanium (Ti), and tin (Sn).

[0029] With reference now to Fig. 3 and Fig. 4 describes a static DC magnetron sputtering device ( Fig. 3) to illustrate a continuous DC magnetron sputtering device ( Fig. 4) for continuously producing the anode electrode according to the present disclosure. In Fig. 3, a DC magnetron sputtering device 200 applies the anode active material layer comprising amorphous silicon to the roughened anode current collector 46. The roughened anode current collector 46 is arranged on a substrate carrier 214 in a process chamber 210. A magnetron cathode 216 with magnets 220 and a target 218 is arranged at a distance from the substrate carrier 214.

[0030] During deposition, a process gas mixture, such as argon (Ar), is introduced from a gas source 222 into the process chamber 210 while AC and / or DC power is supplied. In some examples, a mass flow controller 224 and a valve 226 are used to meter the process gas from the gas source 222 into the process chamber 210. A throttle valve 234 and / or a pump 238 control the pressure in the process chamber 210 and / or evacuate the reactants from the process chamber 210. A DC power source 244 supplies DC voltage to the magnetron cathode 216. An AC power source 246 supplies AC voltage to the magnetron cathode 216.

[0031] During deposition, a target material (e.g., silicon) is ejected from the target 218 and deposited onto the roughened anode current collector 46. Material is also sputtered from an exposed surface of the roughened anode current collector 46. In some examples, a silicon target (e.g., n-type; 99.995%) sputters silicon particles onto a porous anode current collector (e.g., a copper mesh). In some examples, the DC power source 244 provides a DC voltage in a range of 100 V to 1000 V. In some examples, the cathode power of the AC power source 246 is in a range of 0.5 to 30 kW at a frequency in a range of 20 to 200 kHz. In some examples, the current collector width is in a range of 10 to 500 cm. In some examples, the process may be performed two or more times on the same side to increase the thickness of the amorphous silicon layer.

[0032] In some examples, sputtering is performed on a continuous current collector in a roll-to-roll process. The speed of the roll-to-roll process ranges from 2 m / min to 20 m / min. In some examples, the width of the anode current collector ranges from 10 cm to 500 cm. Because this is a solvent-free manufacturing process, no environmental controls for solvent consumption or drying steps to remove the solvent are required. The anode electrode exhibits good mechanical flexibility, which increases durability.

[0033] With reference now to Fig. 4, a continuous DC magnetron sputtering device 300 applies amorphous silicon to a roughened current collector using multiple targets using PVD in a roll-to-roll process. A roll 314 is arranged in a roll-to-roll chamber 310, which feeds a roughened current collector 312. The roughened current collector 312 is guided around a roller 316, around tension rollers 318 and 322, and through a slot 325 in a partition wall 324 (which serves, for example, as a vacuum seal). The current collector 312 enters a magnetron sputtering chamber 330 and onto a roller 340, which serves as a rotating substrate carrier. The roller 340 is grounded. A plurality of sputtering targets 334-1, 334-2, ... and 334-T are arranged circumferentially around a portion of the roller 340, where T is an integer greater than one.

[0034] After the target has sputtered amorphous silicon onto the current collector 312 at the plurality of sputtering targets 334-1, 334-2, ..., and 334-T, an electrode 344 (the current collector 312 and the sputtered amorphous silicon layer) exits the magnetron sputtering chamber 330 through an elongated hole 327 (which serves, for example, as a vacuum seal) and enters the roll-to-roll chamber 310. The electrode 344 passes over idler pulleys 350 and 354, around a roller 358, and is collected on a roller 362.

[0035] The vacuum in the roll-to-roll chamber 310 may be controlled via a valve 370 and a pump 372 connected to an exhaust system 374. The vacuum in the magnetron sputtering chamber 330 may be regulated using a valve 380 and a pump 382 connected to an exhaust system 384. A process gas mixture comprising one or more gases (e.g., argon (Ar)) may be supplied via one or more gas sources, mass flow controllers 292, and / or valves 294.

[0036] The roughened copper current collector (e.g., foil) is delivered using a roll-to-roll approach. In a magnetron sputtering chamber, a silicon layer is continuously deposited onto the roughened copper current collector from multiple silicon targets in an argon atmosphere. After sputtering, the anode electrode is collected on a roll. The process continues on the other side of the current collector to obtain double-sided anode electrodes.

[0037] With reference now to Fig. 5A and Fig. Figure 5B shows the anode electrode during charging and discharging. The damaged spherical surfaces of Si allow for more interfaces with the electrolyte (e.g., solid-state electrolyte) to increase the Li-ion conduction paths, thus increasing the battery's performance. The damaged spherical surfaces help relieve the stresses generated by Si expansion, improving the battery's cyclability.

[0038] The anode electrode described herein does not include the ionic insulating binder that enhances performance. Furthermore, the carbon additive is removed, thus avoiding adverse reactions with the electrolyte (e.g., solid-state electrolyte), thus extending the cell's lifetime.

[0039] With reference now to Fig. 6 and Fig. 7, the anode electrode can be used in battery cells with solid electrolyte, liquid electrolyte and / or gel electrolyte. In Fig. 6, a battery cell includes an anode electrode 540 with an amorphous silicon active layer 542 disposed within a roughened current collector 546. A separator 532 comprises a polymer separator. A cathode layer 520 includes a cathode active material layer 524 and a cathode current collector 526. Liquid electrolyte 550 (e.g., LiPF6 in carbonate) is used.

[0040] In Fig. 7, a battery cell includes an anode electrode 540 with the amorphous silicon active layer 542 disposed on a roughened current collector 546. A separator 562 includes a solid electrolyte. A cathode layer 570 includes a cathode active material layer 574, a solid electrolyte 578, and a cathode current collector 576.

[0041] With reference now to Fig. Figure 8, Scanning electron micrographs of top and side views of the anode electrode. Amorphous silicon columns are shown after formation on the roughened copper current collector.

[0042] With reference now to Fig. 9A and Fig. Figure 9B shows graphs of the X-ray diffraction (XRD) profiles and the Raman spectrum of the anode electrodes. Fig. 9A, the deposited silicon layer is amorphous and does not exhibit any XRD diffraction peaks corresponding to Si. In Fig. 9B, the Raman spectrum shows a peak at 465 cm -1 , which can be assigned to the transverse optical (TO) mode of amorphous silicon (a-Si).

[0043] With reference now to Fig. 10A and Fig. 10B, the graphs show the capacity and percentage capacity retention as a function of cycles for a battery cell with the anode electrode. The anode electrode has a charge of 3.5 mAh / cm 2 The cathode electrode has a charge of 1.41 mAh / cm 2 The cathode active material layer comprises NCM523 as the active material, lithium phosphorus sulfur chloride (LPSCI) and carbon (C) in a ratio of 5:4:04. Fig. 10A is the power rating for the anode electrodes at 25 °C. In Fig. Figure 10B shows the cycling stability of the anode electrodes at 25 °C. The amorphous silicon anode electrodes offer good performance and extended cycle life.

[0044] The foregoing description is merely illustrative and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be embodied in a variety of forms. While this disclosure includes particular examples, the true scope of the disclosure should not be limited thereby, since other modifications will become apparent upon study of the drawings, the specification, and the following claims. It is to be understood that one or more steps within a method may be performed in a different order (or simultaneously) without changing the principles of the present disclosure.Although each of the embodiments described above includes certain features, one or more of those features described with respect to any embodiment of the disclosure may be implemented in any other embodiment and / or combined with features of any other embodiment, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and combinations of one or more embodiments with each other remain within the scope of this disclosure.

[0045] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaged," "coupled," "adjacent," "adjacent," "on top of," "over," "under," and "disposed." When a relationship between a first and a second element is not explicitly described as "direct" in the above disclosure, that relationship may be a direct relationship, with no other intervening elements present between the first and second elements, or it may be an indirect relationship, with one or more intervening elements (either spatial or functional) present between the first and second elements.As used herein, the phrase "A, B, and / or C" should be construed as logical (A ORed with B ORed with C) using a non-exclusive logical OR, rather than as "at least one of A, at least one of B, and at least one of C."

[0046] In the figures, the direction of an arrow, as indicated by the arrowhead, generally indicates the flow of information (e.g., data or instructions) of interest for the representation. For example, if element A and element B exchange a lot of information, but the information passed from element A to element B is relevant for the representation, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is passed from element B to element A. For information sent from element A to element B, element B may further send requests for the information to element A or acknowledge receipt of it.

Claims

[1] A method of manufacturing an anode electrode for a battery cell, comprising: Feeding a roughened anode current collector from a roll-to-roll chamber to a magnetron sputtering chamber; Guiding the roughened anode current collector around a roller in the magnetron sputtering chamber; using T sputtering targets arranged circumferentially around a portion of the roller, sputtering an amorphous silicon layer onto the roughened anode current collector to form an anode electrode, where T is an integer greater than one; and Picking up the anode electrode from the magnetron sputtering chamber into the roll-to-roll chamber. [2] The method of claim 1, wherein the roughened anode current collector is formed of a material selected from a group consisting of copper, stainless steel (SS), nickel (Ni), titanium (Ti), and tin (Sb). [3] The method according to claim 1, wherein the roughened anode current collector has a roughness (Rz) in a range of 0.1 µm to 12 µm. [4] The method according to claim 1, wherein a thickness of the roughened anode current collector is in a range of 0.1 µm to 40 µm. [5] The method according to claim 1, wherein a thickness of the amorphous silicon layer is in a range of 0.1 µm to 20 µm. [6] The method of claim 1, wherein the amorphous silicon layer comprises a plurality of silicon pillars. [7] The method of claim 6, wherein the diameter of the plurality of silicon pillars is in a range of 0.1 µm to 15 µm. [8] The method according to claim 1, wherein the average areal capacity of the anode electrode is in a range of 4 to 30 mAh / cm 2 lies. [9] The method of claim 1, wherein the DC bias voltage of the magnetron sputtering chamber is in a range of 100 V to 1000 V. [10] The method of claim 1, wherein the cathode power of the magnetron sputtering chamber is in a range of 0.5 kW to 30 kW.

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