Method of forming an electrochemical cell with a combination of charge rates

Abstract

Methods of forming an electrochemical cell are described. In some embodiments, the methods can include providing an electrochemical cell having an electrode comprising at least about 20 wt% to about 99 wt% silicon. The methods can include providing a formation charge current to the electrochemical cell at a first rate and a second rate. The first rate can be about C / 100 to about C / 10, and the second rate can be greater than about C / 10.

Description

[0001] Cross-references / citations of related applications are incorporated.

[0002] This application is a divisional application of U.S. Patent Application No. 202080084781.0, filed on December 3, 2020, entitled “Method for Forming Electrochemical Cells by Combination Formation Charge Rate”, and claims priority to U.S. Patent Application No. 16 / 708,013, filed on December 9, 2019.

[0003] field

[0004] This disclosure relates to electrodes, electrochemical cells, and methods for forming electrodes and electrochemical cells. Specifically, this disclosure relates to methods for forming electrochemical cells, including lithium-ion batteries.

[0005] Related technical descriptions

[0006] Lithium-ion batteries typically include a separator and / or electrolyte between the anode and cathode. In one type of battery, the materials for the separator, cathode, and anode are formed as sheets or films, respectively. The sheets of cathode, separator, and anode are stacked or rolled in sequence, with the separator separating the cathode from the anode (e.g., the electrode) to form the battery. For the cathode, separator, and anode to be rolled, each sheet must be sufficiently deformable or flexible to be rolled without failure, such as cracking, breakage, mechanical failure, etc. A typical electrode consists of a layer of electrochemically active material on a conductive metal (e.g., aluminum or copper). For example, carbon can be deposited on the current collector along with an inactive binder material. Carbon is commonly used because it has excellent electrochemical properties and is also conductive. Electrodes can be rolled or cut into blocks and then stacked into a stack. The stack has alternating electrochemically active materials and separators between them. Summary of the Invention

[0007] In some embodiments, a method for forming an electrochemical cell is provided. The method may include providing an electrochemical cell with a rated capacity of 1C and supplying a formation charging current to the electrochemical cell at a constant current of a first rate and a constant current of a second rate. The first rate may be from about C / 100 to about C / 10, and the second rate may be greater than about C / 10. The electrochemical cell may include a first electrode and a second electrode. At least the first electrode may contain at least about 20 wt% to about 99 wt% silicon. The electrochemical cell may also include a separator between the first electrode and the second electrode. The electrochemical cell may include an electrolyte in contact with the first electrode, the second electrode, and the separator.

[0008] In some cases, the first multiplier can be approximately C / 80 to approximately C / 10. For example, the first multiplier can be approximately C / 60 to approximately C / 10. As another example, the first multiplier can be approximately C / 50 to approximately C / 10.

[0009] In some cases, the second multiplier can be less than or equal to about 10C. For example, the second multiplier can be greater than about 0.5C and less than or equal to about 10C. As another example, the second multiplier can be greater than about 1C and less than or equal to about 10C. As yet another example, the second multiplier can be greater than about 1.5C and less than or equal to about 10C.

[0010] In some embodiments, the formation charging current may be provided at a first rate for about 1 minute to about 1,000 minutes. In some embodiments, the formation charging current may be provided at a second rate for about 1 minute to about 1,000 minutes.

[0011] In various methods, providing the formation charging current may include charging to partially form at a first rate. For example, charging to partially form at a first rate may include charging to about 10% to about 50% of the total capacity of the electrochemical cell. As another example, charging to partially form at a first rate may include charging to about 10% to about 30% of the total capacity of the electrochemical cell.

[0012] In various methods, providing the formation charging current may include charging to partially form at a second rate. For example, charging to partially form at a second rate may include charging to about 50% to about 90% of the total capacity of the electrochemical cell. As another example, charging to partially form at a second rate may include charging to about 70% to about 90% of the total capacity of the electrochemical cell.

[0013] In some embodiments, the formation charging current may be provided at a first rate prior to the second rate. In other embodiments, the formation charging current may be provided at a second rate prior to the first rate.

[0014] In some cases, the entire formation of a battery can be completed within a single charge or a single charge / discharge cycle.

[0015] In some methods, providing the formation charging current may include providing the formation charging current until the battery voltage reaches about 4.0 volts to about 4.5 volts. In some instances, providing the formation charging current includes providing the formation charging current at a first rate until 5 to 50% of the nominal capacity, and providing the formation charging current at a second rate until the battery voltage reaches about 4.0 volts to about 4.5 volts.

[0016] In various embodiments, the electrochemical cell may be a lithium-ion battery, and providing the formation charging current may include providing the formation charging current without substantially lithium deposition. In some cases, the first electrode may be an anode. The first electrode may include a silicon-dominant electrode. For example, the first electrode may contain about 30 wt% to about 99 wt%, about 40 wt% to about 99 wt%, about 50 wt% to about 99 wt%, about 60 wt% to about 99 wt%, about 70 wt% to about 99 wt%, or about 80 wt% to about 99 wt% of silicon. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating, schematically, an exemplary method for forming an electrochemical cell according to certain embodiments described herein.

[0018] Figure 2 A comparison of formation voltage curves for two half-cells made with a standard graphite electrode and an exemplary silicon-dominant composite electrode is shown.

[0019] Figure 3 The normalized discharge capacity is shown as a function of the number of cycles of the battery converted with different charging rates.

[0020] Figure 4 The diagram shows the change in charge as a function of voltage divided by the change in voltage (dQ / dV) during the first formation charge cycle of batteries formed at different charge rates. Detailed Implementation

[0021] Formation is a step in the production process of electrochemical batteries such as lithium-ion batteries. This step typically takes place in a factory before the batteries are delivered to the customer. The step generally involves applying current to the battery in such a way as to insert lithium into the negative electrode. This initial “charge” may cause the system to undergo both reversible and irreversible reactions. For stability, it may be desirable to control the reaction to control the interfacial layer formed between the electrode and the electrolyte, called the solid electrolyte interface (SEI), and to remove any gases that form (e.g., in a process called degassing). In some cases, the temperature may be increased to increase the reaction rate. During formation, the potential of the negative electrode typically decreases. When the potential of the negative electrode decreases, it may drop below the stability window of the electrolyte solution. The electrolyte solution can then begin to react with the negative electrode, forming the SEI. Typically, the SEI can reduce and / or minimize further reactions between the negative electrode and the electrolyte solution without preventing lithium ions from migrating to and from the negative electrode. To control the properties of the SEI (and therefore the performance characteristics of the battery), it may be desirable to control the formation process. Formation is typically performed at low currents in environments with precise temperature control, and this combination of long processing times (due to low currents) and expensive equipment (due to precise control) can make formation a significant part of the cost of manufacturing lithium-ion batteries. High currents are generally avoided because they can cause lithium deposition and / or other harmful effects. This is especially true for graphite, which is perhaps the most commonly used anode active material today. Therefore, formation can be one of the most expensive parts of manufacturing (e.g., due to the time spent in the formation process and the equipment used for formation). Many companies are looking to reduce formation time in order to lower capital investment costs.

[0022] This application describes certain methods for forming electrochemical cells, which, for example, can be performed with reduced formation processing time and less complex equipment compared to current methods. Some examples may include providing an electrochemical cell having an electrode (e.g., an anode) comprising silicon (e.g., at least about 20% by weight). Some such electrodes may be advantageous because relatively high currents can be applied during formation without damaging the cell. For example, these electrodes may have relatively high potentials, making lithium deposition and other detrimental effects less likely. Therefore, some methods may include providing the formation charging current with a combination of relatively low charging current (e.g., a relatively slow charging rate, such as about C / 100 to about C / 10) and relatively high charging current (e.g., a relatively fast charging rate, such as greater than about C / 10). Using a relatively fast charging rate can reduce formation time, and using a relatively slow charging rate can allow the formation of a more robust SEI layer than a SEI layer formed solely by a faster formation rate.

[0023] Converted into electric current

[0024] One way to reduce formation time is to increase the battery's charge and discharge rates and reduce the number of cycles the battery undergoes during formation. Unfortunately, batteries with graphite anodes subjected to rapid charge and discharge rates exhibit poor cycle performance. Graphite is a two-dimensional intercalation material, which limits the amount and rate at which lithium can be intercalated into its layered structure.

[0025] Silicon can replace graphite as the dominant anode material because it can withstand rapid charging and discharging, among other benefits. Most electrodes considered "silicon anodes" in industry are graphite anodes with a relatively small amount of silicon added (typically <20%). These graphite-silicon hybrid anodes utilize graphite, which has a lower lithiation voltage compared to silicon; and to utilize graphite, the silicon must be almost completely lithilated. Therefore, these electrodes do not possess the advantages of silicon or silicon composite anodes, where the electrode voltage relative to Li / Li + They can operate at significantly higher voltages than 0 V and are therefore less prone to lithium deposition. Furthermore, these electrodes can exhibit significantly higher excess capacity on silicon compared to the counter electrode, further enhancing robustness at high rates.

[0026] In the various battery designs described herein, the anode may be underutilized. The anode can have excess capacity and higher voltage, offering advantages over other silicon anodes. However, silicon can expand much more than graphite during lithiation, potentially leading to instability of the SEI, silicon particles, and the entire battery after delithiation and repeated cycling. Minimizing the instability caused by the expansion and contraction of silicon particles is desirable to improve the cycle performance of batteries with silicon-dominant anodes. Since formation triggers the initial expansion of silicon and SEI layer growth, adjusting the formation charge rate to increase (e.g., optimize in some cases) different phenomena, such as SEI composition, thickness, and uniformity on the anode, can improve the cycle performance of batteries with silicon-dominant anodes.

[0027] Figure 1 This is a flowchart illustrating, schematically, an example method for forming an electrochemical cell according to certain embodiments described herein. Method 100 for forming an electrochemical cell may include providing an electrochemical cell, as shown in block 110. The electrochemical cell may include a first electrode and a second electrode, a separator between the first and second electrodes, and an electrolyte in contact with the first electrode, the second electrode, and the separator. At least one electrode may contain at least about 20% by weight silicon (e.g., at least about 20% by weight to about 99% by weight silicon).

[0028] Various electrodes of this type, as described herein, can handle relatively high charging currents and / or charging rates without damaging the battery. Therefore, as shown in block 120, method 100 in some embodiments may include providing a first formation charging current (e.g., a constant current formation charging current at a first rate) and a second formation charging current (e.g., a constant current formation charging current at a second rate) to the electrochemical cell. In some cases, the formation charging current may flow to the battery at a first rate of about C / 100 to about C / 10. In some cases, the formation charging current may flow to the battery at a second rate greater than about C / 10.

[0029] Unbound by theory, one reason why the various embodiments of the electrodes (e.g., anodes) described herein can employ relatively high currents is that the electrodes possess relatively high potentials, for example, compared to graphite relative to Li / Li. + In contrast, because the voltages of the various silicon electrodes described in this article are relatively high, the electrodes may not be fully utilized and may have excessive capacity.

[0030] Figure 2 A comparison of formation voltage profiles for two half-cells fabricated using a standard graphite electrode and an exemplary silicon-dominant composite electrode is shown. In both cases, the electrodes were lithium-lithiated to their designed capacity. Figure 2 The data shows that the graphite electrode is relative to Li / Li + The potential drops to approximately 10 mV, while the silicon-dominated composite electrode compared to Li / Li + The potential stabilizes at approximately 70 mV after initial activation. The graphite electrode has a potential of 3.1 mA / cm². 2 The anode is coated with 96% graphite and 4% PVdF. It operates at 0.68 mA / cm². 2 It decreases to 10 mV and then tapers to 0.11 mA / cm. 2 The silicon-dominated composite electrode has a strength of 2.97 mA / cm². 2 80% silicon composite anode. It has a strength of 0.30 mA / cm². 2 The formation is then carried out to the nominal capacity. The relatively low potential of graphite electrodes can be problematic because inhomogeneities in current density, diffusion, or charge transfer rates can create localized regions of low potential where lithium deposition may occur. Conversely, the relatively high potential of silicon-dominated composite electrodes significantly reduces the likelihood of lithium deposition. By Ohm's law, for a given impedance, the relative rate advantage of silicon-dominated composite electrodes over graphite electrodes can be expressed relative to Li / Li + The ratio of characteristic potentials. Therefore, the rate performance of an exemplary silicon-dominated composite electrode can be improved by 7 times relative to a graphite anode (e.g., 70 mV / 10 mV).

[0031] refer to Figure 1 Box 110 in the diagram indicates that the provided electrochemical cell may include at least one electrode, said at least one electrode comprising a silicon-dominant electrode. The electrode may contain at least about 20% by weight of silicon. In some embodiments, the electrode may contain at least about 20% by weight to about 99% by weight of silicon. For example, the weight percentage of silicon may be any value within this range (e.g., about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 95%, about 96%, about 97%, about 98%, about 99%, etc.), or any range within this range, such as any range formed by exemplary values ​​(e.g., about 30% to about 99%, about 40% to about 99%). The electrode may contain 9%, about 50% to about 99%, about 60% to about 99%, about 70% to about 99%, about 80% to about 99%, about 90% to about 99%, about 30% to about 95%, about 40% to about 95%, about 50% to about 95%, about 60% to about 95%, about 70% to about 95%, about 80% to about 95%, about 30% to about 90%, about 40% to about 90%, about 50% to about 90%, about 60% to about 90%, about 70% to about 90%, about 80% to about 90%, etc. The electrode may also contain additives, such as conductive materials (e.g., one or more metals or alloys) and / or graphite active materials. U.S. Patent Application No. 13 / 008,800, entitled "Composite Materials for Electrochemical Storage," filed January 18, 2011, and published on July 21, 2011, under U.S. Patent Application No. 2011 / 0177393; U.S. Patent Application No. 13 / 601,976, entitled "Silicon Particles for Battery Electrodes," filed August 31, 2012, and published on June 19, 2014, under U.S. Patent Application No. 2014 / 0170498; and U.S. Patent Application No. 13 / 601,976, entitled "Silicon Particles for Battery Electrodes"; The U.S. Patent Application No. 13 / 799,405, filed March 13, 2013 and published June 19, 2014, under U.S. Patent Application No. 2014 / 0166939 (each of which is incorporated herein by reference), describes certain embodiments of carbon-silicon composite materials using carbonized polymers and silicon materials that can be used as silicon-dominant electrodes. Other exemplary embodiments of the electrodes are described herein.

[0032] Silicon-dominant electrodes can be used as anodes, cathodes, or both. For example, composite materials can be used as anodes in electrochemical cells (e.g., most conventional lithium-ion batteries); they can also be used as cathodes in some electrochemical couples, for example, with additional additives. In some cases, the electrode voltage can be designed relative to Li / Li + The voltage ranges from approximately 20 mV to approximately 70 mV. Various embodiments of the provided electrochemical cell can be used in secondary batteries (e.g., rechargeable) or primary batteries (e.g., non-rechargeable). The electrochemical cell can have a rated capacity of 1C.

[0033] refer to Figure 1Box 120 in the diagram allows the formation charging current to be provided to the electrochemical cell at a first rate (e.g., constant current) and a second rate (e.g., constant current). In various embodiments, the second rate can be faster than the first rate. For example, the first rate can be a relatively slow rate, and the second rate can be a relatively fast rate. In some embodiments, the formation charging current can be provided at a first rate of about C / 100 to about C / 10. For example, the formation charging current can be provided at a first rate of any charging rate within that range (e.g., about C / 100, about C / 95, about C / 90, about C / 85, about C / 80, about C / 75, about C / 70, about C / 65, about C / 60, about C / 55, about C / 50, about C / 45, about C / 40, about C / 35, about C / 30, about C / 25, about C / 20, about C / 15, about C / 10 ... The formation charging current can be C / 10, or any range within that range, such as any range formed by exemplary values ​​(e.g., about C / 100 to about C / 20, about C / 100 to about C / 30, about C / 100 to about C / 40, about C / 100 to about C / 50, about C / 90 to about C / 10, about C / 80 to about C / 10, about C / 70 to about C / 10, about C / 60 to about C / 10, about C / 50 to about C / 10, etc.). In some embodiments, the formation charging current may be provided at a second multiple greater than about C / 10 (e.g., greater than about C / 5, greater than about C / 2, greater than about 1C, etc.). For example, the formation charging current may be provided at a second multiple of about C / 10 to about 10C. For example, the formation charging current can be provided at a second rate, which is any charging rate within that range (e.g., approximately C / 10, approximately C / 5, approximately 0.5C, approximately 0.7C, approximately 1C, approximately 1.2C, approximately 1.5C, approximately 1.7C, approximately 2C, approximately 2.5C, approximately 3C, approximately 3.5C, approximately 4C, approximately 4.5C, approximately 5C, approximately 7C, approximately 10C, etc.), or any range within that range, such as that provided by [other methods]. Any range of exemplary values ​​(e.g., about C / 10 to about 5C, about C / 5 to about 5C, about 0.5C to about 5C, about 0.7C to about 5C, about 1C to about 5C, about 1.5C to about 5C, about 1.7C to about 5C, about C / 5 to about 10C, about 0.5C to about 10C, about 0.7C to about 10C, about 1C to about 10C, about 1.5C to about 10C, about 1.7C to about 10C, etc.). Other examples are also possible.

[0034] In various embodiments, the formation charging current can be provided at the first rate before the second rate. In other embodiments, the formation charging current can be provided at the second rate before the first rate.

[0035] In various embodiments, during formation, a formation charging current can be supplied to the electrochemical cell with virtually no lithium deposition and / or other undesirable side reactions. Because silicon-dominated electrodes can accept relatively high charge rates, formation can be performed in a shorter time compared to conventional manufacturing. In some embodiments, the formation charging current can be supplied at a first rate for approximately 1 minute to approximately 1000 minutes. For example, the duration of supplying the formation charging current at the first rate can be any duration within this range (e.g., approximately 1 minute, approximately 2 minutes, approximately 3 minutes, approximately 5 minutes, approximately 10 minutes, approximately 20 minutes, approximately 30 minutes, approximately 40 minutes, approximately 50 minutes, approximately 60 minutes, approximately 70 minutes, approximately 75 minutes, approximately 80 minutes, approximately 90 minutes, approximately 100 minutes, approximately 150 minutes, approximately 200 minutes, approximately 250 minutes, approximately 300 minutes, approximately 350 minutes, approximately 400 minutes, approximately 450 minutes, approximately 500 minutes, approximately 550 minutes). The time intervals are approximately 600 minutes, 650 minutes, 700 minutes, 750 minutes, 800 minutes, 850 minutes, 900 minutes, 950 minutes, 1000 minutes, etc., or any range within that range, such as any range formed by exemplary values ​​(e.g., approximately 10 minutes to approximately 1000 minutes, approximately 50 minutes to approximately 1000 minutes, approximately 100 minutes to approximately 1000 minutes, approximately 200 minutes to approximately 1000 minutes, approximately 300 minutes to approximately 1000 minutes, approximately 400 minutes to approximately 1000 minutes). Approximately 500 minutes to approximately 1000 minutes, approximately 10 minutes to approximately 900 minutes, approximately 50 minutes to approximately 900 minutes, approximately 100 minutes to approximately 900 minutes, approximately 200 minutes to approximately 900 minutes, approximately 250 minutes to approximately 900 minutes, approximately 10 minutes to approximately 800 minutes, approximately 50 minutes to approximately 800 minutes, approximately 100 minutes to approximately 800 minutes, approximately 200 minutes to approximately 800 minutes, approximately 250 minutes to approximately 800 minutes, approximately 10 minutes to approximately 750 minutes, approximately 50 minutes to approximately 750 minutes, approximately 100 minutes to Approximately 750 minutes, approximately 200 minutes to approximately 750 minutes, approximately 250 minutes to approximately 750 minutes, approximately 1 minute to approximately 500 minutes, approximately 1 minute to approximately 400 minutes, approximately 1 minute to approximately 300 minutes, approximately 1 minute to approximately 250 minutes, approximately 5 minutes to approximately 500 minutes, approximately 5 minutes to approximately 400 minutes, approximately 5 minutes to approximately 300 minutes, approximately 5 minutes to approximately 250 minutes, approximately 10 minutes to approximately 500 minutes, approximately 10 minutes to approximately 400 minutes, approximately 10 minutes to approximately 300 minutes, approximately 10 minutes to approximately 250 minutes, etc.

[0036] In some implementations, the formation charging current can be provided at a second rate for approximately 1 minute to approximately 1000 minutes. For example, the duration for which the formation charging current is provided at the second rate can be any duration within this range (e.g., approximately 1 minute, approximately 2 minutes, approximately 3 minutes, approximately 5 minutes, approximately 10 minutes, approximately 20 minutes, approximately 30 minutes, approximately 40 minutes, approximately 50 minutes, approximately 60 minutes, approximately 70 minutes, approximately 75 minutes, approximately 80 minutes, approximately 90 minutes, approximately 100 minutes, approximately 150 minutes, approximately 200 minutes, approximately 250 minutes, approximately 300 minutes, approximately 350 minutes, approximately 400 minutes, approximately 450 minutes, approximately 500 minutes, approximately 550 minutes). The time intervals are approximately 600 minutes, 650 minutes, 700 minutes, 750 minutes, 800 minutes, 850 minutes, 900 minutes, 950 minutes, 1000 minutes, etc., or any range within that range, such as any range formed by exemplary values ​​(e.g., approximately 10 minutes to approximately 1000 minutes, approximately 50 minutes to approximately 1000 minutes, approximately 100 minutes to approximately 1000 minutes, approximately 200 minutes to approximately 1000 minutes, approximately 300 minutes to approximately 1000 minutes, approximately 400 minutes to approximately 1000 minutes). Approximately 500 minutes to approximately 1000 minutes, approximately 10 minutes to approximately 900 minutes, approximately 50 minutes to approximately 900 minutes, approximately 100 minutes to approximately 900 minutes, approximately 200 minutes to approximately 900 minutes, approximately 250 minutes to approximately 900 minutes, approximately 10 minutes to approximately 800 minutes, approximately 50 minutes to approximately 800 minutes, approximately 100 minutes to approximately 800 minutes, approximately 200 minutes to approximately 800 minutes, approximately 250 minutes to approximately 800 minutes, approximately 10 minutes to approximately 750 minutes, approximately 50 minutes to approximately 750 minutes, approximately 100 minutes to Approximately 750 minutes, approximately 200 minutes to approximately 750 minutes, approximately 250 minutes to approximately 750 minutes, approximately 1 minute to approximately 500 minutes, approximately 1 minute to approximately 400 minutes, approximately 1 minute to approximately 300 minutes, approximately 1 minute to approximately 250 minutes, approximately 5 minutes to approximately 500 minutes, approximately 5 minutes to approximately 400 minutes, approximately 5 minutes to approximately 300 minutes, approximately 5 minutes to approximately 250 minutes, approximately 10 minutes to approximately 500 minutes, approximately 10 minutes to approximately 400 minutes, approximately 10 minutes to approximately 300 minutes, approximately 10 minutes to approximately 250 minutes, etc.

[0037] In some cases, the formation charging current can provide a longer duration at the first rate compared to the second rate. For example, the formation charging current can provide approximately 500 minutes to approximately 700 minutes at the first rate (e.g., approximately 500 minutes, approximately 510 minutes, approximately 520 minutes, approximately 530 minutes, approximately 540 minutes, approximately 550 minutes, approximately 560 minutes, approximately 570 minutes, approximately 580 minutes, approximately 590 minutes, approximately 600 minutes, approximately 610 minutes, approximately 620 minutes, 630 minutes, approximately 640 minutes, approximately 650 minutes, approximately 660 minutes, approximately 670 minutes, approximately 680 minutes, approximately 69 ... 0 minutes, about 700 minutes, etc.), and at a second rate, about 10 minutes to about 200 minutes (e.g., about 10 minutes, about 20 minutes, about 30 minutes, about 40 minutes, about 50 minutes, about 60 minutes, about 70 minutes, about 80 minutes, about 90 minutes, about 100 minutes, about 110 minutes, about 120 minutes, about 130 minutes, about 140 minutes, about 150 minutes, about 160 minutes, about 170 minutes, about 180 minutes, about 190 minutes, about 200 minutes, etc.).

[0038] In some other cases, the formation charging current can provide a longer duration at a second rate compared to the first rate. For example, the formation charging current can provide approximately 10 minutes to approximately 200 minutes at the first rate (e.g., approximately 10 minutes, approximately 20 minutes, approximately 30 minutes, approximately 40 minutes, approximately 50 minutes, approximately 60 minutes, approximately 70 minutes, approximately 80 minutes, approximately 90 minutes, approximately 100 minutes, approximately 110 minutes, approximately 120 minutes, approximately 130 minutes, approximately 140 minutes, approximately 150 minutes, approximately 160 minutes, approximately 170 minutes, approximately 180 minutes, approximately 190 minutes, approximately 200 minutes, etc.), and at the second rate... Double rate offers approximately 500 minutes to approximately 700 minutes (e.g., approximately 500 minutes, approximately 510 minutes, approximately 520 minutes, approximately 530 minutes, approximately 540 minutes, approximately 550 minutes, approximately 560 minutes, approximately 570 minutes, approximately 580 minutes, approximately 590 minutes, approximately 600 minutes, approximately 610 minutes, approximately 620 minutes, 630 minutes, approximately 640 minutes, approximately 650 minutes, approximately 660 minutes, approximately 670 minutes, approximately 680 minutes, approximately 690 minutes, approximately 700 minutes, etc.).

[0039] In some cases, the formation charging current can be provided at a second rate for a period of time approximately equal to the first rate. For example, the formation charging current can be provided at both the first and second rates, each lasting approximately 1 minute to approximately 100 minutes (e.g., approximately 1 minute, approximately 2 minutes, approximately 3 minutes, approximately 5 minutes, approximately 10 minutes, approximately 20 minutes, approximately 30 minutes, approximately 40 minutes, approximately 50 minutes, approximately 60 minutes, approximately 70 minutes, approximately 80 minutes, approximately 90 minutes, approximately 100 minutes, etc.).

[0040] The formation time for providing charging current at a first rate and a second rate can be a combination of approximately 2 minutes to approximately 2000 minutes, approximately 50 minutes to approximately 1000 minutes, approximately 75 minutes to approximately 750 minutes, etc. By providing formation charging current at a combination of slow and fast charging rates, various embodiments can form robust SEI layer growth (e.g., due to the time period provided at the slow charging rate) and reduce formation time (e.g., due to the time period provided at the fast charging rate).

[0041] In some cases, to further reduce processing time and / or reduce irreversible capacity, the battery may be charged at a first rate and / or a second rate to partially form. For example, the formation charging current may be provided at the first rate to about 5% to about 50% of the battery's total capacity. For example, the formation charging current may be provided at the first rate to any percentage within that range (e.g., about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, etc.), or any range within that range, such as any range formed by exemplary values ​​(e.g., about 5% to about 30%, about 5% to about 40%, about 10% to about 30%, about 10% to about 40%, about 10% to about 50%, about 15% to about 30%, about 15% to about 40%, about 15% to about 50%, about 20% to about 50%, about 30% to about 50%, etc.). In some cases, the formation charging current may be provided at the second rate to about 50% to about 90% of the battery's total capacity. For example, the conversion charging current can be provided to any percentage within that range (e.g., about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, etc.), or any range within that range, such as any range formed by exemplary values ​​(e.g., about 55% to about 90%, about 60% to about 90%, about 70% to about 90%, about 50% to about 80%, about 50% to about 70%, about 50% to about 60%, etc.). Other examples are also possible.

[0042] In various implementations, the entire formation of the battery can be completed within a single charge or a single charge / discharge cycle. The battery can be formed using a constant current / constant voltage (CC / CV) process. For example, a constant charging current can be provided until a certain voltage is reached. As the battery is fully charged, the current can be tapered and / or reduced. In some cases, a formation charging current can be provided until the battery voltage reaches approximately 4.0 volts to approximately 4.5 volts. In some cases, the formation charging current can be provided at a first rate until 5% to approximately 50% of the nominal capacity, and the formation charging current can be provided at a second rate until the battery voltage reaches approximately 4.0 volts to approximately 4.5 volts.

[0043] Electrodes and methods for forming electrodes

[0044] In various embodiments, the electrodes (e.g., anode and cathode) may comprise a carbonized polymer and a silicon material. For example, a mixture comprising a silicon-containing carbon precursor can form a composite material. This mixture may comprise both carbon and silicon, and therefore may be referred to as a carbon-silicon composite, a silicon-carbon composite, a carbon composite, or a silicon composite.

[0045] A typical carbon anode electrode includes a current collector such as a copper sheet. Carbon is deposited onto the current collector along with an inactive binder material. Carbon is commonly used because of its excellent electrochemical properties and its electrical conductivity. Anode electrodes for rechargeable lithium-ion batteries typically have a specific capacity of approximately 200 mAh / g (including the metal foil current collector, conductive additives, and binder material). Graphite, the active material used in most lithium-ion battery anodes, has a theoretical energy density of 372 mAh / g. In contrast, silicon has a high theoretical capacity of 4200 mAh / g. However, silicon expands by more than 300% after lithiation. Due to this expansion, the silicon-containing anode can expand / contract and lose electrical contact with the rest of the anode. Therefore, silicon anodes should be designed to expand while maintaining good electrical contact with the rest of the electrode.

[0046] U.S. Patent Applications No. 13 / 008,800, 13 / 601,976, and 13 / 799,405 (each of which is incorporated herein by reference) describe certain embodiments of carbon-silicon composite materials using carbonized polymers and silicon materials. The carbonized polymer can serve as a buffer against the expansion of silicon particles during cycling, enabling high cycle life. In some embodiments, the resulting electrode can be an electrode composed primarily of active material. For example, the carbonized polymer can form a substantially continuous conductive carbon phase throughout the electrode, as opposed to particulate carbon suspended in a non-conductive binder in a class of conventional lithium-ion battery electrodes. Because the polymer can be transformed into a conductive and electrochemically active matrix, the resulting electrode can be sufficiently conductive, thereby allowing for the omission, minimization, or reduction of metal foil or mesh current collectors in some embodiments. Therefore, certain embodiments of monolithic self-supporting electrodes are disclosed in U.S. Patent Applications No. 13 / 008,800, 13 / 601,976, and 13 / 799,405. The electrode can have a high energy density of about 500 mAh / g to about 3500 mAh / g, which can be attributed to, for example, 1) the use of silicon, 2) the elimination or significant reduction of metal current collectors, and 3) being composed entirely or substantially entirely of active materials.

[0047] Carbon-silicon composites can be formed by forming a mixture containing a precursor and pyrolyzing the precursor to convert it into a carbon phase. In some embodiments, the carbon precursor is a hydrocarbon compound. For example, the precursor may include polyamide-imide, polyamic acid, polyimide, etc. Other precursors include phenolic resins, epoxy resins, and other polymers. The mixture may also contain a solvent. For example, the solvent may be N-methylpyrrolidone (NMP). Other possible solvents include acetone, diethyl ether, γ-butyrolactone, isopropanol, dimethyl carbonate, ethyl carbonate, dimethoxyethane, etc. Examples of precursor and solvent solutions include PI-2611 (HD Microsystems), PI-5878G (HD Microsystems), and VTEC PI-1388 (RBI, Inc.). PI-2611 consists of >60% n-methyl-2-pyrrolidone and 10% to 30% s-biphenyl dianhydride / p-phenylenediamine. PI-5878G consists of >60% n-methylpyrrolidone, 10% to 30% polyamic acid of phenyl pyrrolidone dianhydride / diaminodiphenyl ether, and 10% to 30% aromatic hydrocarbons (petroleum distillates) containing 5% to 10% 1,2,4-trimethylbenzene. In some embodiments, the amount of precursor (e.g., solid polymer) in the solvent is from about 10 wt.% to about 30 wt.%.

[0048] The mixture may contain silicon particles as described herein. The mixture may contain about 5% to about 80% by weight of a precursor and at least about 20% to about 99% by weight of silicon particles. Additional materials may also be included in the mixture. As an example, carbon particles, including graphitic active materials, shredded or ground carbon fibers, carbon nanofibers, carbon nanotubes, and other conductive carbons, may be added to the mixture. Conductive particles may also be added to the mixture. Additionally, the mixture may be mixed to homogenize it.

[0049] In some embodiments, the mixture is cast onto a substrate. In some embodiments, casting includes using gap extrusion, belt casting, or blade casting techniques. Blade casting techniques may include applying a coating to the substrate by using a flat surface (e.g., a blade) controlled at a distance above the substrate. A liquid or slurry may be applied to the substrate, and the blade may be passed over the liquid to spread the liquid on the substrate. The thickness of the coating can be controlled by the gap between the blade and the substrate, as the liquid passes through the gap. Excess liquid may also be scraped off as the liquid passes through the gap. For example, the mixture may be cast onto a substrate comprising a polymer sheet, a polymer roller, and / or a foil or roller made of glass or metal. The mixture may then be dried to remove the solvent. For example, polyamic acid and NMP solution may be dried at about 110°C for about 2 hours to remove the NMP solution. The dried mixture may then be removed from the substrate. For example, an aluminum substrate may be etched off with HCl. Alternatively, the dried mixture may be removed by peeling it off the substrate or by mechanically removing it from the substrate in other ways. In some embodiments, the substrate comprises polyethylene terephthalate (PET), including, for example, Mylar®. In some embodiments, the dried mixture is a film or sheet. In some embodiments, the dried mixture is optionally cured. In some embodiments, the dried mixture may be further dried. For example, the dried mixture may be placed in a hot press (e.g., between graphite plates in an oven). The hot press may be used for further drying and / or curing and to keep the dried mixture flat. For example, a dried mixture from polyamic acid and NMP solution may be hot-pressed at about 200°C for about 8 to 16 hours. Alternatively, the entire process, including casting and drying, may be performed in the form of a roll-to-roll process using standard film processing equipment. The dried mixture may be rinsed to remove any solvent or etchant that may remain. For example, deionized (DI) water may be used to rinse the dried mixture. In some embodiments, belt casting technology may be used for casting. In some embodiments, the mixture can be applied to a substrate using a slot die coating process (e.g., measuring a constant or substantially constant weight and / or volume through a set or substantially set gap). In other embodiments, no substrate is used for casting, and it is not necessary to remove the anode film from any substrate. The dried mixture can be cut or mechanically divided into smaller pieces.

[0050] The mixture further undergoes pyrolysis to convert the polymer precursor into carbon. In some embodiments, the mixture is pyrolyzed in a reducing atmosphere. For example, an inert atmosphere, vacuum, and / or flowing argon, nitrogen, or helium can be used. In some embodiments, the mixture is heated to about 900°C to about 1350°C. For example, polyimide formed from polyamic acid can be carbonized at about 1175°C for about one hour. In some embodiments, the heating and / or cooling rate of the mixture is about 10°C / min. A retainer can be used to hold the mixture in a specific geometry. The retainer can be graphite, metal, etc. In some embodiments, the mixture is held flat. After the mixture is pyrolyzed, tabs can be attached to the pyrolyzed material to form electrical contacts. For example, nickel, copper, or alloys thereof can be used for the tabs.

[0051] In some embodiments, one or more of the methods described herein can be carried out as a continuous process. In some embodiments, casting, drying, possibly curing, and pyrolysis can be carried out as a continuous process. For example, the mixture can be coated onto a glass or metal roller. The mixture can be dried while rotating on the roller to produce a film. The film can be transferred or peeled off in roll form and supplied to another machine for further processing. Extrusion and other industrially known film manufacturing techniques can also be used prior to the pyrolysis step.

[0052] The pyrolysis of the precursor forms pyrolytic carbon and produces one or more types of carbon phases. The term "pyrolytic carbon" refers to carbon formed by pyrolysis. Pyrolytic carbon can include hard carbon and / or soft carbon, but does not include graphite. In some embodiments, the precursor is any material that can be pyrolyzed to form pyrolytic carbon. When the mixture contains one or more additional materials or phases besides the carbonized precursor, composite materials can be produced. In particular, the mixture may contain silicon particles that produce silicon-carbon composite materials (e.g., at least one first phase containing silicon and at least one second phase containing carbon) or silicon-carbon-carbon composite materials (e.g., at least one first phase containing silicon, at least one second phase containing carbon, and at least one third phase containing carbon).

[0053] Silicon particles can increase the specific lithium insertion capacity of composite materials. When silicon absorbs lithium ions, it undergoes a significant volume increase on the order of 300+ volume percentages, which can cause problems with electrode structural integrity. Besides the volume expansion-related issues, silicon is not inherently conductive, but becomes conductive when it forms alloys with lithium (e.g., lithiation). When silicon is delithiated, its surface loses conductivity. Furthermore, the volume reduction during delithiation leads to a loss of contact between the silicon particles and the matrix. This significant volume change also results in mechanical failure of the silicon particle structure, causing it to pulverize. Pulverization and loss of electrical contact make using silicon as an active material in lithium-ion batteries challenging. Reducing the initial size of silicon particles can prevent further pulverization of the silicon powder and minimize the loss of surface conductivity. Furthermore, adding materials to the composite that can elastically deform with changes in the volume of the silicon particles can reduce the chance of losing electrical contact with the silicon surface. For example, the composite material can contain carbon such as graphite, which helps the composite absorb expansion and also allows for lithium ion insertion to increase the storage capacity of the electrode (e.g., if chemically active). Therefore, composite materials can contain one or more types of carbon phases.

[0054] As described herein, silicon can be used as an active material for either the cathode or anode to increase the volumetric energy density and gravimetric energy density of lithium-ion batteries. Various types of silicon materials (e.g., silicon nanopowders, silicon nanofibers, porous silicon, and ball-milled silicon) are viable candidates as active materials for either the negative or positive electrode. As described herein, the amount of silicon provided in the mixture or composite material can be from about 20% by weight to about 99% by weight of the composite material.

[0055] In some embodiments, all, substantially all, or at least some of the silicon particles may have the following particle sizes (e.g., particle diameter or maximum size): less than about 50 μm, less than about 40 μm, less than about 30 μm, less than about 20 μm, less than about 10 μm, less than about 1 μm, about 10 nm to about 50 μm, about 10 nm to about 40 μm, about 10 nm to about 30 μm, about 10 nm to about 20 μm, about 0.1 μm to about 20 μm, about 0.5 μm to about 20 μm, about 1 μm to about 20 μm, about 1 μm to about 15 μm, about 1 μm to about 10 μm, about 10 nm to about 10 μm, about 10 nm to about 1 μm, less than about 500 nm, less than about 100 nm, and about 100 nm. For example, in some embodiments, the average particle size (or average diameter or average maximum size) or median particle size (or median diameter or median maximum size) of the silicon particles can be less than about 50 μm, less than about 40 μm, less than about 30 μm, less than about 20 μm, less than about 10 μm, less than about 1 μm, about 10 nm to about 50 μm, about 10 nm to about 40 μm, about 10 nm to about 30 μm, about 10 nm to about 20 μm, about 0.1 μm to about 20 μm, about 0.5 μm to about 20 μm, about 1 μm to about 20 μm, about 1 μm to about 15 μm, about 1 μm to about 10 μm, about 10 nm to about 10 μm, about 10 nm to about 1 μm, less than about 500 nm, less than about 100 nm, and about 100 nm. In some embodiments, the silicon particles can have a particle size distribution. For example, at least about 95%, at least about 90%, at least about 85%, at least about 80%, at least about 70%, or at least about 60% of the particles may have the particle size described herein.

[0056] In some embodiments, the silicon particles are at least partially crystalline, substantially crystalline, and / or fully crystalline. Furthermore, the silicon particles may or may not be substantially pure silicon. For example, the silicon particles may be substantially silicon, or they may be a silicon alloy. In one embodiment, the silicon alloy comprises silicon as a major component, along with one or more other elements.

[0057] Advantageously, the silicon particles described herein can improve the performance of electrochemically active materials, such as improving capacity and / or cycling performance. Furthermore, electrochemically active materials containing such silicon particles may not experience significant degradation due to lithiation of the silicon particles.

[0058] The amount of carbon obtained from the precursor can be greater than 0 wt% to about 80 wt%, for example, about 1 wt% to about 80%, about 1 wt% to about 70 wt%, about 1 wt% to about 60 wt%, about 1 wt% to about 50 wt%, about 1 wt% to about 40 wt%, about 1 wt% to about 30 wt%, about 5 wt% to about 80 wt%, about 5 wt% to about 70 wt%, about 5 wt% to about 60 wt%, about 5 wt% to about 50 wt%, about 5 wt% to about 40 wt%, about 5 wt% to about 30 wt%, about 10 wt% to about 80 wt%, about 10 wt% to about 70 wt%, about 10 wt% to about 60 wt%, about 10 wt% to about 50 wt%, about 10 wt% to about 40 wt%, about 10 wt% to about 30 wt%, about 10 wt% to about 25 wt%, etc. For example, the amount of carbon obtained from the precursor can be about 1 wt%, about 5 wt%, about 10 wt%, about 15 wt%, about 20 wt%, about 25 wt%, etc. Carbon is obtained by heating a carbon-containing precursor at a temperature sufficient to cause pyrolysis of the precursor; therefore, the carbon is pyrolytic carbon.

[0059] The carbon from the precursor can be hard carbon and / or soft carbon. Hard carbon can be carbon that does not convert to graphite even when heated above 2800°C. The precursor, which melts or flows during pyrolysis, converts to soft carbon at sufficient temperature and / or pressure. In some cases, the precursor can form graphite after further heat treatment (e.g., at 2000°C to 3000°C). Hard carbon is chosen in some embodiments because soft carbon precursors are flowable and soft carbon is mechanically weaker than hard carbon compared to graphite. Possible pyrolytic carbon precursors can include polyimides (or polyimide precursors), other aromatic polyimides, phenolic resins, epoxy resins, poly(p-phenylenevinylene) (PPV), poly(p-phenylene-1,3,4-oxadiazole) (POD), benzimidazole-benzophenanthrenetroline ladder (BBL) polymers, and other polymers with very high melting points or crosslinking. The amount of pyrolytic carbon (e.g., hard carbon and / or soft carbon, but not graphite) in the composite material can be any of the ranges described herein regarding the amount of carbon obtained from the precursor. In some embodiments, the pyrolytic carbon phase is substantially amorphous. In other embodiments, the pyrolytic carbon phase is substantially crystalline. In still other embodiments, the pyrolytic carbon phase includes both amorphous and crystalline carbon. The pyrolytic carbon phase can be the matrix phase in the composite material. Pyrolytic carbon can also be embedded in the pores of silicon-containing additives. Pyrolytic carbon can react with some additives to generate some material at the interface. For example, a silicon carbide layer or an oxygen-containing silicon carbide (Si-CO) layer can be present between the silicon particles and the pyrolytic carbon.

[0060] In some embodiments, after further heat treatment, the graphite is one of the carbon phase types derived from the precursor. In some embodiments, graphite particles are added to the mixture. Graphite can be an electrochemically active material in the battery and an elastically deformable material that can respond to volume changes in silicon particles. For some types of currently commercially available lithium-ion batteries, graphite is a preferred active anode material because it has low irreversible capacity. Additionally, graphite is softer (in some directions) than pyrolytic carbon and can better absorb the volume expansion of silicon additives. In some embodiments, all, substantially all, or at least some of the graphite particles may have a particle size (e.g., diameter or maximum size) of about 0.5 micrometers to about 20 micrometers. In some embodiments, the average particle size (e.g., average diameter or average maximum size) or median particle size (e.g., median diameter or median maximum size) of the graphite particles is about 0.5 micrometers to about 20 micrometers. In some embodiments, the graphite particles may have a particle size distribution. For example, at least about 95%, at least about 90%, at least about 85%, at least about 80%, at least about 70%, or at least about 60% of the particles may have the particle size described herein. In some embodiments, the composite material may contain a quantity of graphite particles greater than 0 wt% and less than about 80 wt%, including 40 wt% to about 75 wt%, about 5 wt% to about 30 wt%, 5 wt% to about 25 wt%, 5 wt% to about 20 wt%, or 5 wt% to about 15 wt%.

[0061] In some embodiments, conductive particles, which may also be electrochemically active, are added to the mixture. Such particles enable more conductive and mechanically deformable composites that can absorb significant volume changes occurring during lithiation and delithiation. In some embodiments, all, substantially all, or at least some of the conductive particles may have a particle size (e.g., diameter or maximum size) of about 10 nanometers to about 7 micrometers. In some embodiments, the average particle size (e.g., average diameter or average maximum size) or median particle size (e.g., median diameter or median maximum size) of the conductive particles is about 10 nm to about 7 micrometers. In some embodiments, the conductive particles may have a particle size distribution. For example, at least about 95%, at least about 90%, at least about 85%, at least about 80%, at least about 70%, or at least about 60% of the particles may have the particle size described herein.

[0062] In some embodiments, the mixture comprises conductive particles in amounts greater than 0 wt% to up to about 80 wt%. In some embodiments, the composite material comprises about 45 wt% to about 80 wt%. The conductive particles can be conductive carbon, including carbon black, carbon fibers, carbon nanofibers, carbon nanotubes, etc. Many carbons considered non-electrochemically active conductive additives become active once pyrolyzed in the polymer matrix. Alternatively, the conductive particles can be metals or alloys, including copper, nickel, or stainless steel.

[0063] After the precursor is pyrolyzed, the resulting carbon material can be a self-supporting monolithic structure. The carbonization of the precursor produces an electrochemically active structure that holds the composite material together. For example, the carbonization precursor can be a substantially continuous phase. Advantageously, the carbonization precursor can be both a structural material and an electrochemically active and conductive material. In some embodiments, the material particles added to the mixture are uniformly or substantially uniformly distributed throughout the composite material to form a homogeneous or substantially homogeneous composite.

[0064] In some embodiments, the composite material and / or electrode do not contain polymers other than trace amounts remaining after precursor pyrolysis. In other embodiments, the composite material and / or electrode do not contain non-conductive binders. The composite material may also include porosity. In some embodiments, the composite material (or membrane) may include a porosity of about 1% to about 70% or about 5% to about 50% on a volumetric porosity basis. For example, the porosity may be about 5% to about 40% on a volumetric porosity basis.

[0065] In some applications, such as those requiring currents exceeding a certain threshold or additional mechanical support, current collectors may be preferred. U.S. Patent Application No. 13 / 333,864, entitled "Electrodes, Electrochemical Cells, and Methods of Forming Electrodes and Electrochemical Cells," filed December 21, 2011, and published June 19, 2014, under U.S. Patent Application No. 2014 / 0170482; U.S. Patent Application No. 13 / 796,922, entitled "Electrodes, Electrochemical Cells, and Methods of Forming Electrodes and Electrochemical Cells," filed March 12, 2013, and published June 19, 2014, under U.S. Patent Application No. 2014 / 0170475; and U.S. Patent Application No. 13 / 796,922, entitled "Methods of Forming Carbon-Silicon Composite Material on a Current...", are relevant examples. The U.S. Patent Application No. 15 / 471,860, filed on March 28, 2017 and published on October 4, 2018, under U.S. Patent Application No. 2018 / 0287129 (each of which is incorporated herein by reference), describes certain embodiments of electrodes including current collectors, electrochemical cells including such electrodes, and methods of forming such electrodes and electrochemical cells.

[0066] In some embodiments, the full capacity of the composite material of the electrodes described herein may not be used during battery use to improve battery life (e.g., the number of charge and discharge cycles before battery failure or performance degradation below usable levels). For example, a composite material having about 70% by weight silicon particles, about 20% by weight carbon from a precursor, and about 10% by weight graphite can have a maximum weight capacity of about 3000 mAh / g, while the composite material may only be used at a weight capacity of about 550 mAh / g to about 1500 mAh / g. Although the maximum weight capacity of the composite material may not be used, using the composite material at a lower capacity can still achieve a higher capacity than some lithium-ion batteries. In some embodiments, the composite material is used at or only at a weight capacity of about 70% of the maximum weight capacity of the composite material. For example, the composite material is not used at a weight capacity of more than about 70% of the maximum weight capacity of the composite material. In other embodiments, the composite material is used at or only at a weight capacity of about 50% or less than about 30% of the maximum weight capacity of the composite material.

[0067] Example

[0068] The following examples are provided to illustrate the benefits of some embodiments of electrodes, electrochemical cells, and methods of forming the same. These examples are discussed for illustrative purposes, but should not be construed as limiting the scope of the disclosed embodiments.

[0069] Figure 3 The normalized discharge capacity in the CC / CV scheme is shown as a function of the number of cycles of the battery formed at different charge rates. The cells used were attached to 15 μm copper foil with a silicon content of 85% by weight and an average loading of 4.2 mg / cm³. 2 The cell was constructed using a silicon composite anode with an average thickness of 93 μm. The cathode was prepared with a concentration of 46 mg / cm³. 2 The average loading and average density of the lithium nickel cobalt manganese (LCM) were coated on a 15 μm aluminum foil with 92% lithium, 4% conductive additives, and 4% PVdF. The electrolyte was a 1.2 M LiPF6 organic carbonate solution. The battery design consisted of 5 layers with overall dimensions of 53 mm × 64 mm × 1.911 mm and a nominal capacity of 720 mAh. The batteries were formed using 3 different formation schemes (3 cells each): A. Charge at 1C to 4.2V until 0.05C, then discharge at 1C to 3.3V.

[0070] Charge the BC / 40 to 4.2V, let it stand for 10 minutes, then discharge it at 1C to 3.3V and let it stand for 10 minutes.

[0071] C. Charge at C / 40 to 25% of the nominal capacity, charge at 1C to 4.2V until 0.05C, discharge at 1C to 3.3V, and let stand for 10 minutes.

[0072] The initial charge was to 4.2V, followed by a 1C discharge to 3.3V. The battery's performance at room temperature at a 2C charge rate and a 0.5C discharge rate relative to Li / Li... + Cycling between 4.2 V and 2.75 V. Formation A is an example of a scheme using a fast charging rate (e.g., providing formation charging current at 1C). Formation B is an example of a scheme using a slow charging rate (e.g., providing formation charging current at C / 40). Formation C is an example of a scheme using a combination of slow and fast rates (e.g., providing formation charging current at both C / 40 and 1C). By including a fast charging portion during formation, the formation time can be shortened. Silicon-dominated anodes can be formed in a fraction of the time used in conventional manufacturing and with less complex equipment. This is possible because silicon-dominated anodes can accept high charging rates during formation without lithium deposition and without causing any undesirable side reactions. It can be formed using a simple constant voltage / constant current (CV / CC) scheme with minimal programming requirements and minimal current control.

[0073] The batteries exhibit very similar capacity retention on a normalized basis, but those with Formation B have a lower initial discharge capacity. Batteries formed with Formation C (charged with a combination of slow and fast rates) demonstrate cycling performance that combines the advantages of both Formation A and Formation B, with a high initial capacity retention and slower capacity decay after more than 150 cycles.

[0074] Using a slow formation charge rate (e.g., C / 100 to C / 10) can be advantageous for battery cycle performance because it allows for the formation of a more robust SEI layer than if formed only by a faster formation rate (e.g., 1C or greater). SEI formation can be important because it affects the battery's subsequent cycle performance.

[0075] Figure 4The diagram shows the logarithmic scale of charge change as a function of voltage divided by voltage change (e.g., dQ / dV) during the first formation charge cycle of a battery using two different formation rates. The dashed line represents the dQ / dV of a battery formed at a 1C formation charge rate, while the solid line represents the dQ / dV of a battery formed at a combination of 1C and C / 40 charge rates. The solid line, with peaks from 1V to 4V, indicates that SEI formation occurs within this potential window during charging. However, in this voltage region, the dashed line has a lower peak amplitude than the solid line, indicating that less SEI formation occurs. In various embodiments, using a combination of slow and fast formation charge rates to form the battery can combine the advantages of robust SEI layer growth with the time savings of rapid formation. Furthermore, the formation can be modified depending on the application. In some cases, the formation can be modified (e.g., on-demand or batch) to meet the desired characteristics of the final application. For example, using a single-cell design, the battery performance can be significantly altered with different formation rates and can be used to customize performance.

[0076] Various embodiments have been described above. Although the invention has been described with reference to these specific embodiments, the description is intended to be illustrative and not limiting. Various modifications and applications can be made by those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for forming an electrochemical cell, the method comprising: An electrochemical cell is provided, the electrochemical cell comprising: A first electrode and a second electrode, wherein at least the first electrode comprises at least about 20% by weight to about 99% by weight silicon; The partition between the first electrode and the second electrode; and An electrolyte in contact with the first electrode, the second electrode, and the separator, wherein the electrochemical cell has a rated capacity of 1C; and A formation charging current is provided to the electrochemical cell at a first rate of constant current and a second rate of constant current, wherein the first rate is about C / 100 to about C / 10 and the second rate is greater than about C / 10.

2. The method of claim 1, wherein the first multiplier is about C / 80 to about C / 10.

3. The method of claim 1, wherein the second multiplier is less than or equal to about 10C.

4. The method of claim 1, wherein the second multiplier is greater than about 0.5C and less than or equal to about 10C.

5. The method of claim 1, wherein the formation charging current is provided at the first multiplier for about 1 minute to about 1,000 minutes.

6. The method of claim 1, wherein the formation charging current is provided at the second multiplier for about 1 minute to about 1,000 minutes.

7. The method of claim 1, wherein providing the formation charging current comprises charging to a portion of the formation at the first multiplier.

8. The method of claim 7, wherein the first rate is charged to partially form up to about 10% to about 50% of the total capacity of the electrochemical cell.

9. The method of claim 1, wherein providing the formation charging current comprises charging to a portion of the formation at the second rate.

10. The method of claim 9, wherein the second rate is used to charge to approximately 50% to approximately 90% of the total capacity of the electrochemical cell.

11. The method of claim 1, wherein the formation charging current is provided at the first multiplier before the second multiplier.

12. The method of claim 1, wherein the formation charging current is provided at the second rate prior to the first rate.

13. The method of claim 1, wherein the entire formation of the battery is completed within a single charge or a single charge / discharge cycle.

14. The method of claim 1, wherein providing the formation charging current comprises providing the formation charging current until the battery voltage reaches about 4.0 volts to about 4.5 volts.

15. The method of claim 1, wherein providing the formation charging current comprises providing the formation charging current at the first rate up to 5% to 50% of the nominal capacity, and providing the formation charging current at the second rate up to the battery voltage reaching 4.0 volts to about 4.5 volts.

16. The method of claim 1, wherein the electrochemical cell is a lithium-ion battery, and providing the formation charging current includes providing the formation charging current with substantially no lithium deposition.

17. The method of claim 1, wherein the first electrode is an anode.

18. The method of claim 1, wherein the first electrode comprises a silicon-dominant electrode.

19. The method of claim 1, wherein the first electrode comprises about 30% to about 99% by weight of the silicon.

20. The method of claim 19, wherein the first electrode comprises about 40% to about 99% by weight of the silicon.

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