JP2022550102A - Method and system for silicon-based lithium-ion cells with controlled lithiation of silicon - Google Patents

Abstract

Systems and methods for silicon-based lithium-ion cells with controlled lithiation of silicon include a cathode, an electrolyte, and an anode. The anode comprises lithiated silicon at a post-discharge level configured to exceed a minimum threshold level, the minimum threshold for lithiation being 3% silicon lithiation. The level of silicon lithiation after charging the battery may range from 30% to 95% silicon lithiation, from 30% to 75% silicon lithiation, from 30% to 65% silicon lithiation, or from 30% to 50% silicon lithiation range. The level of silicon lithiation after discharging the battery ranges from 3% to 50% silicon lithiated, 3% to 30% silicon lithiated, or 3% to 10% silicon lithiated. . The minimum threshold level is the lithiation level below which the cycle life of the battery is degraded. Electrolytes include liquids, solids, or gels.

Description

CROSS REFERENCE/INCORPORATION BY REFERENCE TO RELATED APPLICATIONS This application is the subject of U.S. patent application serial no. 16/584,574, the contents of which are incorporated herein by reference.

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 silicon-based lithium-ion cells with controlled lithiation of silicon.

Conventional approaches to battery anodes are costly, cumbersome, and/or inefficient, for example, they are complex and/or time consuming to implement and can limit battery life.

Further limitations and disadvantages of the conventional traditional approach can be found by comparing such a system with several aspects of the present disclosure described in the remainder of this application, with reference to the drawings. will be apparent to those skilled in the art.

For a silicon-based lithium ion cell with controlled lithiation of silicon substantially as shown in and/or described in connection with at least one drawing, as fully described by the claims system and/or method.

These and other advantages, aspects and novel features of the present disclosure, as well as details of illustrative embodiments thereof, will become more fully understood from the following description and drawings.

1 is a diagram of a battery with a silicon-based anode, according to an exemplary embodiment of the present disclosure; FIG. 4 illustrates exemplary lithiation and delithiation processes for silicon-based anodes, according to exemplary embodiments of the present disclosure. 4 shows voltage profile curves for a lithium-ion battery with a silicon-based anode, according to an exemplary embodiment of the present disclosure; 4 illustrates an exemplary lithiation and delithiation process of a prelithiated silicon-based anode, according to an exemplary embodiment of the present disclosure; 4 shows voltage profile curves for a lithium-ion battery with a pre-lithiated silicon-based anode, according to an exemplary embodiment of the present disclosure; 4 illustrates a process of pre-lithiated silicon anode, according to an exemplary embodiment of the present disclosure; 4 shows fast charge capability of cells with silicon-based anodes, according to exemplary embodiments of the present disclosure. 4 is a plot showing cell cycle life versus charge rate for a silicon-based anode cell, according to an exemplary embodiment of the present disclosure;

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

The development of portable electronic devices and the electrification of transportation are driving the need for high performance electrochemical energy storage. Small (<100 Wh) to large scale (>10 KWh) devices primarily use lithium-ion (Li-ion) batteries due to their superior performance over other rechargeable batteries.

Anode 101 and cathode 105 may comprise electrodes, along with current collectors 107A and 107B, where the electrodes may comprise plates or films within or including the electrolyte material, where the plates may be physical to contain the electrolyte. It can provide conductive contacts to barriers and external structures. In other embodiments, the anode/cathode plates are immersed in the electrolyte, while the outer casing provides a containment vessel for the electrolyte. Anode 101 and cathode are electrically coupled to current collectors 107A and 107B, which are metal or other materials for providing electrical contact to the electrodes and physical support for the active material in forming the electrodes. of conductive material.

Although the configuration shown in FIG. 1 shows the battery 100 in discharge mode, in a charging configuration the load 107 can be replaced with a charger and the process reversed. In one class of batteries, the separator 103 is generally a film material made of an electrically insulating polymer, e.g. or vice versa. Typically, the separator 103, cathode 105, and anode 101 materials are individually formed into sheets, films, or foils coated with an active material. The sheets of cathode, separator and anode are then laminated or rolled together with separator 103 separating cathode 105 and anode 101 to form battery 100 . In some embodiments, the separator 103 is a sheet and typically utilizes winding methods and lamination in its manufacture. In these methods, the anode, cathode, and current collectors (eg, electrodes) can comprise films.

In an exemplary scenario, battery 100 may include solid, liquid, or gel electrolytes. Separator 103 is preferably made of ethylene carbonate ( _EC ), fluoroethylene carbonate (FEC) _, propylene carbonate (PC ₎ , dimethyl carbonate (DMC ₎ , ethylmethyl It is not soluble in typical battery electrolytes such as compositions that may contain carbonate (EMC), diethyl carbonate (DEC), and the like. Separator 103 can be wetted or soaked with a liquid or gel electrolyte. Further, in an exemplary embodiment, separator 103 does not melt below about 100-120° C. and exhibits sufficient mechanical properties for battery applications. A battery in operation may experience expansion and contraction of the anode and/or cathode. In an exemplary embodiment, separator 103 can expand and contract by at least about 5 to 10% without failure and can be flexible.

Separator 103 can be sufficiently porous to allow ions to pass through the separator when wetted with, for example, a liquid or gel electrolyte. Alternatively (or additionally), the separator can imbibe electrolyte through gelation or other processes without significant porosity. The porosity of separator 103 is also generally not porous enough to allow anode 101 and cathode 105 to conduct electrons through separator 103 .

Anode 101 and cathode 105 comprise the electrodes of battery 100 and provide electrical connections to devices for transferring charge during charge and discharge states. Anode 101 may comprise, for example, silicon, carbon, or a combination of these materials. A typical anode electrode includes a current collector such as a copper sheet and includes a carbon material. Carbon is often used because it has excellent electrochemical properties and is also electrically conductive. Anode electrodes currently used in rechargeable lithium-ion batteries typically have a specific capacity of about 200 milliamp-hours per gram. Graphite, the active material used in many 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. To increase the volumetric and gravimetric energy density of lithium-ion batteries, silicon can be used as the cathode or anode active material. A silicon anode can be formed, for example, from a silicon composite containing greater than 50% silicon.

In an exemplary scenario, anode 101 and cathode 105 store ions used for charge separation, such as lithium. In this example, the electrolyte carries positively charged lithium ions from anode 101 to cathode 105 in discharge mode and vice versa through separator 105 in charge mode, as shown for example in FIG. Lithium ion migration creates free electrons at anode 101, which create a charge at positive current collector 107B. Current then flows from the current collector through the load 109 to the negative current collector 107A. Separator 103 blocks the flow of electrons inside battery 100 .

While the battery 100 is discharging and supplying current, the anode 101 releases lithium ions through the separator 103 to the cathode 105, transferring electrons from one side to the other through the coupled load 109. generate flow. The opposite occurs when the battery is being charged, lithium ions being released by the cathode 105 and being received by the anode 101 .

The materials selected for anode 101 and cathode 105 are important to battery 100 reliability and energy density. The energy, power, cost, and safety of current Li-ion batteries need to be improved to compete with internal combustion engine (ICE) technology and enable the widespread adoption of electric vehicles (EV). The high energy density, high power density, and improved safety of lithium-ion batteries are due to functionally non-flammable electrolytes with high voltage stability and interfacial compatibility with the electrodes, high capacity and high voltage cathodes, and high This is achieved through the development of capacitive anodes. Additionally, materials with low toxicity are beneficial as battery materials to reduce process costs and promote consumer safety.

State-of-the-art lithium-ion batteries typically employ graphite-based anodes as the intercalation material for lithium. However, silicon-based anodes offer improvements compared to graphite-based lithium ion batteries. Silicon exhibits a higher gravimetric capacity (3579 mAh/g vs. 372 mAh/g for graphite) and volumetric capacity (2194 mAh/L vs. 890 mAh/L for graphite). Further, silicon-based anodes have a voltage of about 0.3-0.4 V vs. Having a low Li/Li ^{2 +} lithiation/delithiation voltage plateau allows the open circuit potential to be maintained to avoid undesirable Li plating and dendrite formation. Although silicon exhibits excellent electrochemical activity, achieving stable cycle life of silicon-based anodes is difficult due to the large volume change of silicon during lithiation and delithiation. The silicon region can lose electrical contact from the anode because its low electrical conductivity plus large volume changes separate the silicon from the surrounding material within the anode.

In addition, large silicon volume changes exacerbate solid electrolyte interface (SEI) formation, which can further lead to electrical isolation and thus capacity loss. The expansion and contraction of the silicon particles during charge/discharge cycles pulverize the silicon particles and increase the specific surface area. As the silicon surface area changes and increases during cycling, the SEI is repeatedly decomposed and reformed. Therefore, during cycling, SEI continues to accumulate around the crushed silicon regions, resulting in thick electronic and ionic insulating layers. This accumulated SEI increases electrode impedance, reduces electrode electrochemical reactivity, and adversely affects cycle life.

Due to its high specific capacity, abundance and low cost, silicon is a promising active material for lithium ion anodes. However, large volume changes (>300% volume change) during lithiation and delithiation cause mechanical degradation of the electrode and unstable SEI, leading to electrode swelling and poor cell cycle life. Silicon-based anodes perform best when the lithiation of the silicon anode is maintained within a specific range. To achieve such performance, the cell can be designed according to the criteria shown in FIG. 2, for example. Silicon materials have upper and lower lithiation limits for desired cell operation. The upper limit _xH corresponds to the maximum lithium content that silicon can accept without significantly affecting cycle life. The lower limit x _L corresponds to the minimum threshold level, ie the minimum residual lithium content that must remain in the silicon structure to maximize cycle life. Below this level of lithiation, the cycle life decreases from cycle to cycle. The fully lithiated silicon stage at room temperature is Li _3.75 Si, which corresponds to a maximum theoretical capacity of 3579 mAh/g for silicon, which is much higher than that of graphite (372 mAh/g).

The cell can be designed so that the maximum amount of lithium coming from the cathode, _xC , does not exceed _xH . Similarly, the minimum amount of lithium remaining in the anode after discharge (x _D ) must be higher than x _L . This disclosure describes a cell design in which silicon is partially prelithiated and then lithiated/delithiated during operation to achieve target cell capacity and energy. Pre-lithiation means that lithium is incorporated into the silicon during manufacture of the anode, as opposed to the lithiation/delithiation that occurs during charging and discharging of the battery, and this pre-lithiation during discharge. is not delithiated.

FIG. 2 shows an exemplary lithiation and delithiation process of a silicon-based anode, according to exemplary embodiments of the present disclosure. Referring to FIG. 2, the lithiation levels of the cathode and silicon-based anode are shown. The lithiation level of the cathode indicates the amount Δ _Li that can migrate to the anode in the charging process, increasing the lithiation level of the anode from x _D to x _C . The lithiation level of the anode is given on a scale of 0 to 3.75, with 3.75 indicating the fully lithiated stage Li _3.75 Si of silicon. The quantity Δ _Li can be a function of the number of charge carriers in the cathode and the cathode discharge cutoff voltage. Therefore, in this example, the lithiation of the anode is controlled by the cutoff voltage and should be kept above x _L for best cycle life. The discharged lithiation level _xD is a function of the anode and cathode irreversible charges Qirr _{, the anode} and _{Qirr, the cathode} , and the cut-off voltage, and the charged lithiation level _xC is the number of charges in the material. is a function.

FIG. 3 shows voltage profile curves for a lithium-ion battery with a silicon-based anode, according to an exemplary embodiment of the present disclosure. Referring to FIG. 3, the voltage profile curves for the anode and cathode, the vertical line with arrows indicating the full cell voltage, and the ampere-hour cell capacity on the x-axis for these various full cell voltages are shown.

In this example, the total charge capacity of the cathode is half the total capacity of the anode. During discharge, the cell voltage can be controlled such that the amount of lithium remaining at the anode is higher than the critical amount _xL , as described with respect to FIG. For this particular cell, the cell capacity at 2.7V is 5.963mAh, the cell capacity at 3.1V is 4.555mAh, which is 76.4% of the total capacity, and the cell capacity at 3.2V is The cell capacity at 3.3V is 3.638mAh, corresponding to 61.0% of the capacity, and the cell capacity is 3.136mAh, corresponding to 52.6% of the total capacity.

FIG. 4 shows an exemplary lithiation and delithiation process of a prelithiated silicon-based anode, according to exemplary embodiments of the present disclosure. Referring to FIG. 4, the lithiation level ranges for cathode 401 and silicon-based anode 403 are shown. This example shows another way to control the amount of lithium (x _D ) remaining in the anode after discharge without the need to limit the cell voltage during discharge. This is either pre-lithiation of the anode or use of a sufficiently high irreversible capacity cathode such that _xD remains higher than _xL regardless of the cell's discharge voltage. As before, the lithiation level of the anode is given on a scale of 0 to 3.75, 3.75 indicating the fully lithiated stage of silicon Li _3.75 Si.

The cathode lithiation level in FIG. 4 shows the amount Δ _Li 405 that can be transferred to the anode 403 in the charging process as described in FIG. so that prelithiation ensures that the lithiation level exceeds x _L regardless of the cutoff voltage utilized. In this example, pre-lithiation allows for maximum utilization of the cathode capacity while staying within x _L and x _H limits.

FIG. 5 shows voltage profile curves for a lithium-ion battery with a pre-lithiated silicon-based anode, according to an exemplary embodiment of the present disclosure. Referring to FIG. 5, there are shown anode and cathode voltage profile curves, a vertical line with arrows indicating full cell voltage, and ampere-hour cell capacity on the x-axis at various full cell voltages. In addition, (1) "lost" lithium, (2) "active" lithium or lithium storage, and (3) prelithiation are shown.

With prelithiation of the anode (3), the voltage curve of the anode extends to a higher capacity with a peak at 11 mAh compared to the anode without prelithiation in FIG. For this particular cell with 20% prelithiation, the cell capacity at 2.7 V is 6.297 mAh, at 3.1 V it is 5.793 mAh, corresponding to 92% of the total capacity, and at 3.2 V it is 79 mAh of the total capacity. 5.000 mAh, corresponding to .4%, and 3.306 mAh, corresponding to 52.5% of the total capacity at 3.3V, indicating a significant improvement over the non-prelithiated cells. .

Furthermore, in addition to improved cell capacity, prelithiation also enables 1) controlled expansion and contraction of silicon during charge and discharge cycles of lithium-ion cells, which leads to cracking, shattering of silicon particles; 2) controlled silicon expansion/contraction and silicon anode voltage window reduces cell capacity degradation during cycle life; 3) good cycle life and limited cell maximizing cathode capacity utilization in lithium-ion cells using silicon as the anode material while maintaining the expansion of the Fast charging is enabled, which allows high rate charging and cycling of the cells as described with respect to FIGS.

FIG. 6 illustrates a pre-lithiated silicon anode process, according to an exemplary embodiment of the present disclosure. As shown in FIG. 6, the process begins at step 601 where, for example, a silicon-based anode can be pre-lithiated to a lithiation level between 3% and 95%. A battery or cell may be formed in step 603 with a pre-lithiated silicon anode, cathode, and electrolyte.

In step 605, the anode is lithiated with lithium from the cathode until the lithiation level reaches _xC (held below _xH ) to avoid adversely affecting the cycle life of the battery. A battery can be charged. As described above with respect to FIG. 4, the total amount of lithium transferred can be Δ _Li . In the first example, the range of _xC is from 1.125 to 3.5625, which corresponds to 30% to 95% silicon lithiation, with 3.75 being the maximum lithiation of silicon. In a second example, the range of _xC is from 1.125 to 3.1875, which corresponds to a silicon lithiation of 30% to 85%. In a third example, the range of _xC is from 1.125 to 2.8125, which corresponds to a silicon lithiation of 30% to 75%. In a fourth example, the range of _xC is 1.125 to 2.4375, which corresponds to 30% to 65% silicon lithiation. In a fifth example, the range of _xC is 1.125 to 1.875, which corresponds to 30% to 50% silicon lithiation.

In step 607, the cell may be delithiated to a level _xD , where the anode remains greater than _xL due to prelithiation, and discharged such that the lithium returns to the cathode. In the first example, _xD ranges from 0.12 to 1.875, which corresponds to 3% to 50% residual lithium on silicon. In a second example, the range of _xD is 0.12 to 1.5, which corresponds to 3% to 40% residual lithium on silicon. In a third example, _xD ranges from 0.12 to 1.125, which corresponds to 3% to 30% residual lithium on silicon. In a fourth example, the range of _xD is 0.12 to 0.75, which corresponds to 3% to 20% residual lithium on silicon. In the first example, the range of _xD is 0.12 to 0.375, which corresponds to 3% to 10% residual lithium on silicon.

In step 609, if the cell voltage is still acceptable, ie, the cell is not at the end of its cycle life, the process can return to step 605 and be charged and discharged again.

FIG. 7 illustrates fast charging capability of cells with silicon-based anodes, according to exemplary embodiments of the present disclosure. Please refer to FIG. Referring to FIG. 7, charging curves for a cell with a conventional graphite anode and a cell with a pre-lithiated silicon-based anode at charge rates of 4C, 5.6C and 10C are shown. . As indicated by the plot, silicon-based anode cells can be charged at very high rates. Therefore, the lithiation level of silicon is controlled by the cell design and/or the best use of the silicon anode. Lithium storage is required for best cell performance, either by utilizing the cathode in the manner described with respect to FIGS. can be formed by

FIG. 8 is a plot showing cell cycle life versus charge rate for a silicon-based anode cell, according to an exemplary embodiment of the present disclosure; As shown by the nearly collinear plots, there is essentially no difference in cell life for cells charged at a 4C rate compared to cells charged at 0.5C. Both cells retain 92% of their capacity up to 500 cycles.

Exemplary embodiments of the present disclosure describe methods and systems for silicon-based lithium-ion cells with controlled lithiation of silicon. A battery may include a cathode, an electrolyte, and an anode. The anode may contain silicon lithiated at a post-discharge level configured to exceed a minimum threshold level, the minimum threshold for lithiation being 3% silicon lithiation. The silicon lithiation level after discharge can be configured by the anode discharge voltage. The post-discharge silicon lithiation level may be constituted by the pre-lithiation level of silicon. The silicon lithiation level after discharge can be constituted by the irreversible discharge capacity of the cathode. The level of silicon lithiation after charging the battery may range from 30% to 95% silicon lithiated, from 30% to 75% silicon lithiated, from 30% to 65% silicon lithiated, or from 30% to 50% silicon lithiated. It can range from silicon lithiation. The level of silicon lithiation after discharging the battery can range from 3% to 50% silicon lithiated, from 3% to 30% silicon lithiated, or from 3% to 10% silicon lithiated. A minimum threshold level may be a lithiation level below which the cycle life of the battery is degraded. Electrolytes may include liquids, solids, or gels.

In another exemplary embodiment, a method and system for an anode for use in a battery is described, the anode comprising silicon that is lithiated above a minimum threshold level upon discharge when incorporated into a lithium ion battery. , the lithiation level of silicon after discharge is constituted by the discharge voltage of the anode or the pre-lithiation level of silicon.

As used herein, the term "circuit" refers to physical electronic components (i.e., hardware) as well as hardware that constitutes, is executed by, and/or otherwise , means software and/or firmware (“code”), which may be associated with hardware. As used herein, for example, a particular processor and memory may include a first "circuitry" in executing a first line or lines of code, and executing a second line or lines of code. When implemented, it may include a second "circuitry". As used herein, "and/or" means any one or more items in the list linked by "and/or." By way of example, "x and/or y" means any element of the set of three elements {(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" is a set of seven elements {(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 term "for example" refers to a list of one or more non-limiting examples, instances, or illustrations. As used herein, a circuit or device is defined as a circuit or device whether or not its function is disabled or disabled (e.g., due to user-configurable settings, factory adjustments, etc.). is "operable" to perform a function as long as it contains the necessary hardware and code (if necessary) to perform that function.

Although the present invention has been described with reference to particular embodiments, it will be appreciated by those skilled in the art that various changes can be made and equivalents substituted without departing from the scope of the invention. Yo. 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. Accordingly, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention include all embodiments falling within the scope of the appended claims.

Claims (26)

A battery comprising a cathode, an electrolyte and an anode,
wherein the anode comprises silicon lithiated at a level configured to exceed a minimum threshold level after discharge;
A battery wherein the minimum threshold lithiation is 3% silicon lithiation. 2. The battery of claim 1, wherein the lithiation level of silicon after discharge is constituted by the anode discharge voltage. 2. The battery of claim 1, wherein the lithiation level of silicon after discharge is ensured to exceed a minimum threshold level by pre-lithiation of silicon. 2. The battery of claim 1, wherein the lithiation level of silicon after discharge is constituted by the irreversible discharge capacity of the cathode. 2. The battery of claim 1, wherein the silicon lithiation level after charging of the battery ranges from 30% to 95% silicon lithiation. 2. The battery of claim 1, wherein the silicon lithiation level after charging of the battery ranges from 30% to 75% silicon lithiation. 2. The battery of claim 1, wherein the silicon lithiation level after charging of the battery ranges from 30% to 65% silicon lithiation. 2. The battery of claim 1, wherein the silicon lithiation level after charging of the battery ranges from 30% to 50% silicon lithiation. 2. The battery of claim 1, wherein the level of silicon lithiation after discharge of the battery ranges from 3% to 50% silicon lithiation. 2. The battery of claim 1, wherein the level of silicon lithiation after discharge of the battery ranges from 3% to 30% silicon lithiation. 2. The battery of claim 1, wherein the level of silicon lithiation after discharge of the battery ranges from 3% to 10% silicon lithiation. 2. The battery of claim 1, wherein the minimum threshold level is a lithiation level below which the cycle life of the battery is degraded. 2. The battery of claim 1, wherein said electrolyte comprises a liquid, solid, or gel. forming a battery comprising an anode, a cathode, and an electrolyte, wherein the anode comprises silicon;
charging the battery to lithiate the anode;
discharging the battery, wherein the anode lithiation level remains above a minimum threshold level after discharge, the minimum threshold lithiation being 3% silicon lithiation;
A method, including 15. The method of claim 14, comprising configuring the lithiation level of silicon after discharge by the anode discharge voltage. 15. The method of claim 14, comprising ensuring that the lithiation level of silicon after discharge exceeds a minimum threshold level using pre-lithiation of silicon. 15. The method of claim 14, comprising configuring the lithiation level of silicon after discharge by the irreversible discharge capacity of the cathode. 15. The method of claim 14, wherein the lithiation level of silicon after charging the battery ranges from 30% to 95% lithiation of silicon. 15. The method of claim 14, wherein the lithiation level of silicon after charging the battery ranges from 30% to 75% lithiation of silicon. 15. The method of claim 14, wherein the lithiation level of silicon after charging the battery ranges from 30% to 65% lithiation of silicon. 15. The method of claim 14, wherein the lithiation level of silicon after charging the battery ranges from 30% to 50% lithiation of silicon. 15. The method of claim 14, wherein the lithiation level of silicon after discharging the battery ranges from 3% to 50% lithiation of silicon. 15. The method of claim 14, wherein the lithiation level of silicon after discharging the battery ranges from 3% to 30% lithiation of silicon. 15. The method of claim 14, wherein the lithiation level of silicon after discharging the battery ranges from 3% to 10% lithiation of silicon. 15. The method of claim 14, wherein the minimum threshold level is a lithiation level below which battery cycle life is degraded. An anode for use in a battery, said anode comprising silicon that is lithiated above a minimum threshold level upon discharge when incorporated into a lithium ion battery, wherein the level of lithiation of silicon after discharge is equal to said An anode configured by the discharge voltage of the anode or by the pre-lithiation level of silicon.

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