Method and system for improved performance of cells containing silicon anodes via anodization

Abstract

A system and method for improved performance of cells containing silicon anodes via formation can include a cathode, an electrolyte, and a silicon-containing anode. The battery can be subjected to a formation process that includes one or more cycles of charging the battery at a 1C rate to 3.8 volts or greater until the current in the battery reaches C / 20, and discharging the battery to 2.5V or less. The battery can include a lithium-ion battery. The electrolyte can include a liquid, solid, or gel. The anode can include more than 70% silicon. The battery can be discharged until the current reaches 0.2C. The battery can be discharged at a 1C rate or a 0.2C rate. The battery can be in a rest period between charging and discharging.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS / INCORPORATION BY REFERENCE] This application claims priority to U.S. Patent Application No. 16 / 549,926, filed August 23, 2019, which is incorporated herein by reference in its entirety.

[0002] Aspects of the present disclosure relate to energy generation and storage. More specifically, certain embodiments of the present disclosure relate to methods and systems for improved performance of cells including silicon anodes via formation. [Background technology]

[0003] Conventional approaches to battery anodes can be costly, cumbersome, and / or inefficient—for example, they can be complex and / or time-consuming to implement and can limit the lifespan of the battery.

[0004] Further limitations and disadvantages of conventional and traditional approaches will become apparent to those skilled in the art by comparing such systems with certain aspects of the present disclosure described in the remainder of this application with reference to the drawings. Summary of the Invention [Means for solving the problem]

[0005] As more fully set forth in the claims, a method and system for improved performance of cells including silicon anodes via chemical formation substantially as shown in and / or described in connection with at least one of the drawings.

[0006] These and other advantages, aspects and novel features of the present disclosure, as well as details of illustrated embodiments thereof, will be more fully understood from the following description and drawings. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram of a battery with an ultra-high voltage cobalt-free cathode according to an exemplary embodiment of the present disclosure. [Figure 2] 1 shows the cycling performance of a lithium-ion battery with a silicon anode using conventional formation cycled between 4.2 V and 3.2 V in a first cycle scenario according to an exemplary embodiment of the present disclosure. [Figure 3] 10 shows the cycling performance of a lithium-ion battery with a silicon anode using conventional formation cycled between 4.2 V and 3.2 V in a second cycle scenario according to an exemplary embodiment of the present disclosure. [Figure 4] 1 illustrates a process flow for a formation process for a battery with a silicon anode, according to an exemplary embodiment of the present disclosure. [Figure 5] 1 shows the cycling performance of a lithium-ion battery with a silicon-containing anode using a new chemistry cycled between 4.2 V and 3.2 V in a first cycle scenario according to an exemplary embodiment of the present disclosure. [Figure 6] 1 shows the cycling performance of a lithium-ion battery with a silicon-containing anode using a new chemistry cycled between 4.2 V and 3.2 V in a first cycle scenario according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] Figure 1 is a diagram of a battery according to an exemplary embodiment of the present disclosure. Referring to Figure 1, a battery 100 is shown comprising a separator 103 sandwiched between an anode 101 and a cathode 105, and current collectors 107A and 107B. Also shown is a load 109 coupled to battery 100, illustrating an example when battery 100 is in a discharge mode. In this disclosure, the term "battery" may be used to refer to a single electrochemical cell, multiple electrochemical cells formed into a module, and / or multiple modules formed into a pack.

[0009] The anode 101 and cathode 105, together with current collectors 107A and 107B, may comprise electrodes, which may comprise plates or films in or containing an electrolyte material, and the plates may provide conductive contact to an external structure as well as a physical barrier to contain the electrolyte. In other embodiments, the anode / cathode plates are immersed in the electrolyte, while an outer casing provides containment of the electrolyte. The anode 101 and cathode are electrically coupled to current collectors 107A and 107B, which may comprise a metal or other conductive material to provide physical support for the active material in the electrode formation as well as electrical contact to the electrode.

[0010] The configuration shown in FIG. 1 depicts the battery 100 in a discharging mode, but in a charging configuration, the load 107 can be replaced with a charger and the process can be reversed. In one class of batteries, the separator 103 is generally a film material, made, for example, from an electrically insulating polymer, that is sufficiently porous to allow ions to pass through the separator 103 while preventing electrons from flowing from the anode 101 to the cathode 105 or vice versa. Typically, the separator 103, cathode 105, and anode 101 materials are individually formed into sheets, films, or active material-coated foils. The cathode, separator, and anode sheets are then stacked or rolled to form the battery 100, with the separator 103 separating the cathode 105 and anode 101. In some embodiments, the separator 103 is a sheet, and its manufacture generally utilizes winding and lamination methods. In these methods, the anode, cathode, and current collectors (e.g., electrodes) may comprise films.

[0011] In an exemplary scenario, battery 100 can include a solid, liquid, or gel electrolyte. Separator 103 is preferably insoluble in typical battery electrolytes, such as compositions that may include ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like, with LiBF, LiAsF, LiPF, and LiClO dissolved therein. Separator 103 may be wetted with or immersed in a liquid or gel electrolyte. Furthermore, in exemplary embodiments, separator 103 does not melt below approximately 100-120°C and exhibits sufficient mechanical properties for battery applications. During operation, the battery may experience expansion and contraction of the anode and / or cathode. In exemplary embodiments, separator 103 can expand and contract by at least approximately 5-10% without failure and may also be flexible.

[0012] The separator 103 may be sufficiently porous to allow ions to pass through it once wetted, for example, with a liquid or gel electrolyte. Alternatively (or additionally), the separator may absorb electrolyte through gelation or other processes without being significantly porous. Also, the porosity of the separator 103 is generally not too great, as long as the anode 101 and cathode 105 can transfer electrons through the separator 103.

[0013] The anode 101 and cathode 105 comprise electrodes for the battery 100, providing electrical connections to the device for charge transfer during charging and discharging. In an exemplary scenario, the cathode may include nickel oxide. The anode 101 may include, for example, silicon, carbon, or a combination of these materials. A typical anode electrode includes a carbon material with a current collector, such as a copper plate. Carbon is often used because of its excellent electrochemical properties and electrical conductivity. Anode electrodes currently used in rechargeable lithium-ion cells typically have a specific capacity of approximately 200 milliampere-hours per gram. Graphite, the active material used in most lithium-ion battery anodes, has a theoretical energy density of 372 milliampere-hours per gram (mAh / g). In comparison, silicon has a high theoretical capacity of 4200 mAh / g. Silicon can be used as the active material in the cathode or anode to increase the volumetric and gravimetric energy densities of lithium-ion batteries. The silicon anode may be formed, for example, from a silicon composite material containing more than 50% silicon.

[0014] In an exemplary scenario, the anode 101 and cathode 105 store ions, such as lithium, used for charge separation. In this example, the electrolyte transports positively charged lithium ions from the anode 101 to the cathode 105 in a discharge mode and vice versa through the separator 105 in a charge mode, as shown, for example, in FIG. 1 . The movement of lithium ions creates free electrons in the anode 101, which create a charge on the positive current collector 107B. Current then flows from the current collector through the load 109 to the negative current collector 107A. The separator 103 blocks the flow of electrons within the battery 100.

[0015] While the battery 100 is discharging and supplying electrical current, the anode 101 releases lithium ions through the separator 103 to the cathode 105, causing electrons to flow from one side to the other through the coupled load 109. When the battery is charging, the reverse occurs, with lithium ions being released from the cathode 105 and accepted by the anode 101.

[0016] The materials selected for the anode 101 and cathode 105 are important for the reliability and energy density possible for the battery 100. To compete with internal combustion engine (ICE) technology and enable widespread adoption of electric vehicles (EVs), the energy, power, cost, and safety of current lithium-ion batteries must be improved. High energy density, high power density, and improved safety for lithium-ion batteries can be achieved by developing high-capacity and high-voltage cathodes, high-capacity anodes, and functional, non-flammable electrolytes with high-voltage stability and interfacial compatibility with the electrodes. Furthermore, less toxic materials are beneficial for battery materials to reduce processing costs and promote consumer safety.

[0017] Rechargeable lithium-ion batteries typically comprise an anode (negative electrode), a cathode (positive electrode), a separator, an electrolyte, and a housing. After assembly, lithium-ion batteries typically undergo a specific process called formation, in which a series of electrical, thermal, and physical actions are performed on the cell to initialize it before it is shipped outside the factory. One important aspect of the initial charge, in particular, is that it is designed to form a beneficial solid electrolyte interface (SEI) layer on the anode to prevent excessive reduction of the electrolyte on the anode surface.

[0018] For lithium-ion batteries containing graphite as the primary anode active material, formation consists of four steps, although many formation regimes are more covert and complex: a slow charge to a voltage greater than 3.5 V to promote SEI layer formation on the graphite anode, rest, discharge to either a specific voltage for cell capacity measurement or a specific shipping voltage, and a final rest step. For lithium-ion batteries with graphite anodes, the initial slow charge step is often considered the most critical step in formation, enabling good cycling and storage performance. However, for lithium-ion batteries with silicon-containing anodes (especially those in which silicon is the only or primary active material), such conventional formation results in poor performance under certain cycling conditions.

[0019] FIG. 2 shows the cycling performance of a lithium-ion battery with a silicon anode using conventional formation cycled between 4.2 V and 3.2 V in a first cycle scenario according to an exemplary embodiment of the present disclosure. Referring to FIG. 2, the cycling performance of a lithium-ion battery with silicon as the anode, where the cell is formed using conventional formation, is shown. Formation in this case is performed for four cycles, while most commercial formation procedures are performed for one cycle or less. Formation in this case is performed with a low discharge cutoff voltage of 3.3 V. For each cycle, the cell is charged to 4.2 V at a 1 C rate until the current reaches C / 20, and then the cell is discharged to 3.3 V. The C rate is a measure of the rate at which a battery is charged or discharged relative to its maximum capacity. A 1 C discharge rate means that the discharge current discharges the battery's nominal rated capacity in one hour. For a battery with a capacity of 100 amps / h, this corresponds to a discharge current of 100 amps in one hour. For this battery, a 5 C rate is 500 amps, and a C / 2 rate is 50 amps. The rest period in each cycle includes a period of no charge or discharge, i.e., no load, and can be any time required for the battery to reach a steady state. Examples of such periods include 10 minutes, 15 minutes, or even 30 minutes or more. In other scenarios, the rest period can be several hours. At least 10 minutes is a reasonable minimum.

[0020] The anode in this example is a silicon-dominant anode, e.g., a film with Si>70%, the cathode is NCA mixed with conductive additives & PVDF, and the electrolyte is LiPF6 dissolved in a carbonate blend. To measure discharge capacity loss with cycling, i.e., cycle life, the cell is charged and discharged between 4.2 V and 3.2 V (Scenario-1). In this scenario, the lithium-ion battery loses ~20% of its capacity after 200 cycles. Generally, for most commercial applications, a capacity loss of <20% after 500-1000 cycles is desired.

[0021] 3 shows the cycling performance of a lithium-ion battery with a silicon anode using conventional chemistry cycled between 4.2 V and 3.2 V in a second cycle scenario according to an exemplary embodiment of the present disclosure. In this scenario, Scenario-2, the cell design is the same as Scenario-1. However, in Scenario-2, the lithium-ion battery with a silicon anode has a unique phenomenon where, when the cell is discharged to a voltage below 3.2 V, capacity loss accelerates during cycling to 3.2 V, with capacity regain occurring every 100 cycles.

[0022] Note that in both Scenario-1 and Scenario-2, the lithium-ion cells are cycled between 4.2 V and 3.2 V, but in Scenario-2, there are deeper discharge cycles for every 100 cycles where the discharge voltage is below 3.2 V. These results demonstrate that conventional chemistries can result in significant variations in cycling performance. The cycling performance in both Scenario-1 and Scenario-2 demonstrates that conventional chemistries can cause premature failure of lithium-ion cells with silicon-containing anodes. Such performance is unacceptable in practical applications, potentially resulting in functional defects in the final product.

[0023] 4 illustrates a process flow for a formation process for a battery with a silicon anode according to an exemplary embodiment of the present disclosure. In an exemplary scenario, the cathode may include a nickel-containing oxide. Referring to FIG. 4, the process begins at step 401, where a battery is assembled with an anode, a cathode, a separator, an electrolyte, and a housing. As noted above, the term "battery" may be used to refer to a single electrochemical cell, multiple electrochemical cells formed into a module, and / or multiple modules formed into a pack.

[0024] The process continues with step 403, where the battery is charged beyond a certain voltage / charge, step 405, where the battery is placed in a resting state where it is neither charged nor discharged for a time interval, and step 407, where the battery is discharged below a threshold voltage. In step 409, if this cycle is the last cycle, the process ends with end step 411; however, if there are multiple cycles, the process returns to step 403 for another charge / rest / discharge cycle. Table 1 shows different formation sequences that can be used for silicon anode batteries, with rests used between each charge / discharge step. The main theme of this process is that all sequences force the cell to a substantially fully discharged state (e.g., around 2.5 V for a nickel cathode-based system).

[0025] [Table 1]

[0026] One aspect of the above charge / rest / discharge cycle is that the cell may be charged over a certain amount to remove lithium from the silicon before cycling, and then fully discharged over a certain amount. The amount charged and discharged may correspond to voltage. The charge voltage may need to be greater than 3.8V, 4.0V, or 4.1V. The discharge voltage needs to be less than 2.5V. The charge capacity may need to be greater than 80% of the cell's total reversible capacity, and the discharge capacity may need to be less than 23% of the remaining capacity.

[0027] FIG. 5 shows the cycling performance of a lithium-ion battery with a silicon-containing anode using the new formation according to an exemplary embodiment of the present disclosure, cycled between 4.2 V and 3.2 V in the first cycle scenario. Referring to FIG. 5, a plot of discharge capacity versus cycle number is shown. The plot shows that the cycling performance of a lithium-ion battery with a silicon-containing anode in cycle scenario-1 is improved when the new formation method described above is used. With a conventional formation process, a silicon-containing anode battery experiences a 20% drop in discharge capacity after approximately 200 cycles. However, with the improved formation cycle described with reference to FIG. 4, the battery lasts for more than 750 cycles before losing 20% ​​of its capacity. This corresponds to a 275% improvement in cycle life.

[0028] FIG. 6 shows the cycling performance of a lithium-ion battery with a silicon-containing anode using the new formation according to an exemplary embodiment of the present disclosure, cycled between 4.2 V and 3.2 V in the first cycle scenario. Referring to FIG. 6, a plot of discharge capacity versus cycle number is shown. FIG. 6 shows that when the new formation method described with reference to FIG. 4 is used, the cycling performance of a lithium-ion battery with an anode containing silicon in cycle scenario-2 is improved. In the exemplary scenario, the cathode may include a nickel-containing oxide. When the new formation method is used, the phenomenon of capacity loss and rapid capacity recovery is eliminated. Comparing FIG. 5 and FIG. 6, it can be seen that the variation in cycling performance between scenario-1 and scenario-2 is significantly reduced by using the new formation method described in the present disclosure.

[0029] In an exemplary embodiment of the present disclosure, a method and system for improved performance of cells containing silicon anodes through formation is described. The system may include a cathode, an electrolyte, and a silicon-containing anode, and the battery is subjected to a formation process including one or more cycles of charging the battery at a 1 C rate to above 3.8 volts until the current in the battery reaches C / 20, and discharging the battery to below 2.5 volts. The battery may include a lithium-ion battery. The electrolyte may include a liquid, solid, or gel. The anode may include greater than 70% silicon. The battery may be discharged until the current reaches 0.2 C. The battery may be discharged at a 1 C rate. The battery may be discharged at a 0.2 C rate. The battery may be in a rest period between charging and discharging.

[0030] In another exemplary embodiment, a method and system for improved performance of cells containing silicon anodes through chemical formation is described. The method may include charging a battery containing an anode, a cathode, and an electrolyte, where the anode comprises silicon, at a 1C rate to 4.2 volts or greater until the current in the battery reaches C / 20, and discharging the battery at a 1C rate to X percentage of charge capacity, where X is in the range of 0.77 to 0.99. The battery may comprise a lithium-ion battery. The electrolyte may comprise a liquid, solid, or gel. The anode may comprise greater than 70% silicon.

[0031] As used herein, the terms “circuits” and “circuitry” refer to physical electronic components (i.e., hardware) and any software and / or firmware (“code”) that may comprise, be executed by, or otherwise be associated with the hardware. As used herein, for example, a particular processor and memory may comprise a first “circuit” when executing a first line or lines of code, and a second “circuit” when executing a second line or lines of code. As used herein, “and / or” means any one or more of the items in the list joined by “and / or.” As an example, “x and / or y” means any element of the 3-element set {(x), (y), (x, y)}. In other words, “x and / or y” means “one or both of x and y.” As another example, "x, y, and / or z" means any element of the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. In other words, "x, y, and / or z" means "one or more of x, y, and z." As used herein, the term "exemplary" means serving as a non-limiting example, instance, or illustration. As used herein, the terms "e.g.," and "for example" begin a list of one or more non-limiting examples, instances, or illustrations. As used herein, a circuitry or device is "operable" to perform a function whenever the circuitry or device contains the necessary hardware and code (if any) to perform the function, regardless of whether the functionality of the function has been disabled (e.g., by a user-configurable setting, a factory trim, etc.).

[0032] While the invention has been described with reference to particular embodiments, those skilled in the art will recognize that various modifications can be made and equivalents substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but will include all embodiments falling within the scope of the appended claims. [Explanation of symbols]

[0033] 100 batteries 101 Anode 103 Separator 105 cathode 107A, 107B current collectors 109 Load

Claims

1. A battery comprising an anode, an NCA-based cathode, and an electrolyte, wherein the anode comprises greater than 70% silicon, CC charging the battery at a 1C rate from 3.8 volts to 4.2 volts and CV charging until the current in the battery reaches C / 20; placing the battery in a resting state where it is neither charging nor discharging; Discharging the battery to below 2.5V; Including, A method for forming a battery, wherein the charge capacity is greater than 80% of the total reversible capacity of said battery and the discharge capacity is less than 23% of the remaining capacity.

2. The method of claim 1 , wherein the battery comprises a lithium ion battery.

3. The method of claim 1 , wherein the electrolyte comprises a liquid, a solid, or a gel.

4. 10. The method of claim 1, wherein the battery is discharged until the current reaches 0.2 C.

5. 10. The method of claim 1, wherein the battery is discharged at a 1C rate.

6. 10. The method of claim 1, wherein the battery is discharged at a 0.2 C rate.

7. A battery comprising an anode, an NCA-based cathode, and an electrolyte, wherein the anode comprises greater than 70% silicon, CC charging the battery at a 1C rate from 3.8 volts to 4.2 volts and CV charging until the current in the battery reaches C / 20; placing the battery in a resting state where it is neither charging nor discharging; Discharging the battery at a 1C rate to X percentage of charge capacity, where X is in the range of 0.77 to 0.99; Including, A method for forming a battery, wherein the charge capacity is greater than 80% of the total reversible capacity of said battery and the discharge capacity is less than 23% of the remaining capacity.

8. The method of claim 7 , wherein the battery comprises a lithium ion battery.

9. The method of claim 7 , wherein the electrolyte comprises a liquid, a solid, or a gel.

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