Electrode design to improve lithium-ion battery safety

Abstract

The present disclosure relates to an electrode design for improving the safety of lithium-ion batteries. The lithium-ion battery includes: a cathode; an anode having a main active material, conductive carbon, a binder and a reserve material; and a separator located between the cathode and the anode. The reserve material has a reaction potential between the lithium reaction potential and the main active material reaction potential. The reserve material is configured to intercalate lithium at the reaction potential in response to the main active material being fully intercalated to inhibit lithium plating on the anode.

Description

Technical Field

[0001] The present disclosure relates to electrodes for lithium-ion batteries, and in particular, to a reserve material for improving the safety of the electrodes. Background Art

[0002] Lithium-ion (Li-ion) batteries or cells have become an integral part of most devices from smartphones to electric vehicles. While they offer high energy and power density, they present potential safety risks due to the presence of flammable liquid electrolytes that can cause fires under certain extreme conditions.

[0003] Conventional Li-ion batteries typically include a positive electrode (cathode), a negative electrode (anode), a separator, and an electrolyte. Current collectors are typically attached to each electrode in order to extract current from the battery. In conventional Li-ion batteries, the anode typically includes graphite with a capacity of about 375 mAh / g as the main active material. Graphite has a low discharge voltage (or reaction potential), which provides a large voltage difference between the graphite itself and the cathode, so graphite has a relatively high power and energy density. During charging of a conventional lithium-ion battery containing a graphite anode, lithium ions are embedded in the graphite structure at a low potential (about 0.1 V) relative to lithium (and lithium ions). This process typically continues until all available lithium ions from the cathode are embedded in the graphite and the cell reaches 100% state of charge (SOC) (or is fully embedded), as shown in Figure 1.

[0004] In a properly designed cell, the anode capacity is intentionally designed to exceed the available lithium provided by the cathode so that all the lithium can be completely contained in the graphite. However, during low temperature charging or high rate charging, the potential of the anode in a conventional cell can drop below 0.1V, or even below 0V, resulting in lithium plating on the surface of the anode, as shown in Figure 1. One of the main safety risks of lithium plating is the internal short circuit between the electrodes caused by the formation of lithium filaments (dendrites) that pierce the separator and ultimately reach the cathode. Although lithium plating can occur in any part of the anode structure, it is more likely to occur at the interface between the separator and the anode, especially at the sharp edges or protrusions on the surface of the anode or separator. Due to poor cell design, lithium plating that forms dendrites can occur on the anode surface, especially when the cell is charged at low temperatures and high charging rates.

[0005] In addition to the safety risks at low temperatures and high charging rates, the reduced capacity of graphite can result in it becoming insufficient to accommodate all of the circulating lithium. Thus, lithium plating can also lead to capacity loss and increased impedance in the cell. Summary of the invention

[0006] According to an embodiment, a lithium ion battery is disclosed. The lithium ion battery includes: a cathode; an anode having a main active material, conductive carbon, a binder and a reserve material; and a separator located between the cathode and the anode. The reserve material has a reaction potential between the lithium reaction potential and the main active material reaction potential. The reserve material is configured to intercalate lithium at the reaction potential in response to the main active material being fully intercalated to inhibit lithium plating on the anode.

[0007] According to one or more embodiments, the reaction potential of the reserve material may be between about 0 volts and 0.1 volts. The reaction potential of the reserve material may be between about 0.005 volts and 0.1 volts. The reserve material may be SrO, Mn4N, K2SO4, CaCl2, CaF2, SrF2, Ag, Mg or Zn. In some embodiments, the reserve material may be irreversibly embedded or deintercalated with lithium. In other embodiments, the reserve material may be reversibly embedded or deintercalated with lithium. In one or more embodiments, the reserve material may be mixed with a main active material, conductive carbon and a binder. The reserve material may form a layer on the surface of the anode between the anode and the separator.

[0008] According to another embodiment, a lithium ion battery is disclosed. The lithium ion battery includes: a cathode; an anode having a main active material, conductive carbon, a binder, and a reserve material; and a separator located between the cathode and the anode. The reserve material of the anode has a reaction potential with lithium between about 0 volts and 0.1 volts. The reserve material is configured to intercalate lithium at the reaction potential to inhibit lithium plating on the anode.

[0009] According to one or more embodiments, the reserve material may be mixed with the main active material, the conductive carbon and the binder. In other embodiments, the reserve material may form a layer on the surface of the anode between the anode and the separator. In one or more embodiments, the reserve material may be SrO, Mn4N, K2SO4, CaCl2, CaF2, SrF2, Ag, Mg or Zn. The reaction potential of the reserve material may be between about 0.005 volts and 0.1 volts. In some embodiments, the reserve material may be reversibly embedded or de-embedded with lithium. In other embodiments, the reserve material may be irreversibly embedded or de-embedded with lithium.

[0010] According to an embodiment, a method of operating a lithium ion battery is disclosed. The method includes: in response to a main active material in an anode of the battery being fully intercalated and the anode potential of the battery dropping below the main active material potential, intercalating lithium into an anode reserve material. The anode reserve material has a reaction potential between the lithium reaction potential and the main active material potential to inhibit lithium plating on the anode.

[0011] According to one or more embodiments, the reaction potential of the anode reserve material may be between about 0 volts and 0.1 volts. In some embodiments, the anode may include an anode reserve material mixed with a main active material, conductive carbon, and a polymer binder. In other embodiments, the anode reserve material may form a layer disposed on the surface of the anode between the anode and the separator. The anode reserve material may be SrO, Mn4N, K2SO4, CaCl2, CaF2, SrF2, Ag, Mg, or Zn. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1A , Figure 1B and Figure 1C Schematic diagram of the charging process of a conventional lithium-ion cell at 0% SOC, 100% SOC, and greater than 100% SOC.

[0013] Figure 2 is a schematic diagram of a lithium-ion cell according to an embodiment.

[0014] Figure 3A , Figure 3B and Figure 3C 1 is a schematic diagram of the charging process of a lithium-ion cell at 0% SOC, 100% SOC and greater than 100% SOC according to an embodiment.

[0015] Figure 4A is a schematic diagram of a lithium-ion cell according to another embodiment.

[0016] Figure 4B yes Figure 4A A detailed view of a portion of a schematic diagram.

[0017] Figure 5A , Figure 5B and Figure 5C 1 is a schematic diagram illustrating the volume change of a lithium-ion cell during a charging process at 0% SOC, 100% SOC, and greater than 100% SOC, respectively, according to an embodiment.

[0018] Figure 6 is a graph of potential versus state of charge for various N / P ratios.

[0019] Fig. 7A and Figure 7B is a graph of potential versus state of charge for different types of active materials.

[0020] Figure 8 It is a graph of potential versus state of charge with theoretical potential and overpotential of reserve active material. DETAILED DESCRIPTION

[0021] As required, detailed embodiments of the present invention are disclosed herein; however, it will be understood that the disclosed embodiments are merely examples of the invention, and that the invention may be implemented in a variety of and alternative forms. The figures are not necessarily drawn to scale; certain features may be exaggerated or minimized to show details of particular components. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to variously implement the present invention.

[0022] Conventional lithium-ion battery electrodes operate by the intercalation of lithium ions, where lithium ions are extracted from the anode and migrate to the cathode during discharge, and from the cathode and migrate to the anode during charge. Figures 1A to 1C , showing the charging process of a conventional lithium-ion battery 100. The conventional lithium-ion battery 100 includes a positive electrode (cathode) 110, a separator 120, a negative electrode (anode) 130, and an electrolyte (not shown). A current collector (not shown) is typically attached to each electrode in order to extract current from the battery. In the conventional lithium-ion battery 100, the anode 130 typically includes graphite as a main active material as well as a conductive material (such as conductive carbon) and a binder (such as a polymer binder). As shown in FIG. Figure 1A As shown in FIG. 1 , at 0% state of charge (SOC), lithium (lithium ions) 140 are in the cathode 110. During charging, the lithium 140 is intercalated into the graphite of the anode 130. Figure 1B As shown in , at 100% SOC, lithium 140 is completely embedded in the graphite in the anode 130. Figure 1C As shown in , when the SOC exceeds 100%, the conventional lithium-ion battery 100 undergoes lithium plating 145 on the anode 130. Due to the operating conditions of the conventional lithium-ion battery 100 (such as low temperature or high charging rate), the potential drops to a potential lower than that of graphite, and because the lithium 140 is completely embedded in the anode 130, the lithium 140 forms dendrites due to its plating in the interface between the anode 130 and the separator 120. As the lithium plating 145 grows, the dendrites may pierce the separator 120 and reach the cathode 110, thereby causing a dangerous short circuit in the conventional lithium-ion battery 100.

[0023] According to one or more embodiments, a lithium ion battery design for reducing lithium plating at the anode is disclosed. The anode includes another active material referred to as a reserve active material or a reserve material, and the other active material exhibits an intercalation potential, alloying potential or reaction potential with lithium between the potential of the main active material (graphite) and the potential of lithium metal, and has the ability to react with most of the total available lithium at this potential. Although graphite is disclosed as the main active material, graphite is not intended to be restrictive, and any main active material known to those skilled in the art can be used according to the embodiments. Although the intercalation potential, alloying potential and reaction potential can have thermodynamic meanings, the term "reaction potential" is used hereinafter to include each potential. When the main active material is graphite, the reserve material has a main active material reaction potential (or reaction potential) between the lithium reaction potential (about 0 volts) and the graphite reaction potential (about 0.1 volts). The reserve material exhibits a reaction potential with lithium between about 0 V and 0.1 V, such that when the cell potential drops at 100% SOC (when graphite is fully intercalated), the reserve material intercalates lithium, thereby inhibiting lithium plating on the anode. The reserve material may exhibit an irreversible reaction or a reversible reaction with lithium (such that the reserve material intercalates and deintercalates lithium). The reserve material may be integrated into a lithium-ion cell as a layer between the anode and the separator ( Figure 2 ), or the reserve material can be mixed directly with the graphite particles into the anode itself ( FIG. 4A to FIG. 4B ). Non-limiting examples of stock materials are listed in Table-1:

[0024]

[0025]

[0026] According to one or more embodiments, Figure 2 As shown in , a lithium-ion battery (or cell) 200 includes a cathode 210, a separator 220, and an anode 230. The anode 230 includes, but is not limited to, a primary active material such as graphite, a conductive material, and a binder. The conductive material may be, but is not limited to, conductive carbon, such as amorphous carbon. The binder may be, but is not limited to, a polymer binder. The anode also includes a reserve active material or reserve material 250. In an embodiment, the reserve material 250 is provided as a layer on the surface of the anode 230 at the interface of the separator 220 and the anode 230.

[0027] FIG. 3A to FIG. 3C The lithium-ion battery 200 is shown at 0% SOC ( Figure 3A )、100%SOC( Figure 3B ) and greater than 100% SOC ( Figure 3C) under the charging process. When the anode 230 of the lithium-ion battery 200 is Figure 3B When lithium 240 is fully intercalated, as in a conventional lithium-ion cell, the charge potential at anode 230 can be driven to over 100% SOC due to poor design or due to excessive capacity loss. Figure 3C As shown in , beyond 100% SOC, the potential at the anode 230 containing the reserve material 250 will drop to the insertion potential of the reserve material 250 rather than the main active material, at which potential the lithium ions will begin to react with the reserve material 250 to insert lithium 240 into the reserve material 250 layer rather than being plated as lithium metal on the surface of the anode 230. Assuming an unlimited amount of lithium is delivered from the cathode 210 to the anode 230, this process will continue beyond 100% SOC until all of the reserve material 250 is used, and only then will the potential of the cell 200 drop to 0V and cause lithium plating. Compared to conventional lithium-ion batteries, for cells 200 in which the capacity of the cathode 210 is greater than but close to the capacity of the anode 230, the integration of the reserve material 250 can help reduce the amount of plating.

[0028] FIG. 4A to FIG. 4B A lithium ion battery 400 according to another embodiment is shown. The lithium ion battery 400 includes a cathode 410, a separator 420, and an anode 430. The anode 430 includes, but is not limited to, a main active material 452 such as graphite, a conductive material 454, and a binder (not shown). The conductive material 454 can be, but is not limited to, conductive carbon, such as amorphous carbon. The binder can be, but is not limited to, a polymer binder. The anode 430 also includes a reserve active material or reserve material 450. The reserve material 450 is mixed in the anode 430 with the main active material 452, the conductive material 454, and the binder. Figure 4B A detailed description of the particles of the anode 430 is shown in FIG. When the reserve material 450 is mixed into the anode 430, the reserve material 450 is activated whenever the local potential reaches the reaction potential of the reserve material 450, regardless of the conditions at other locations in the anode 430. Therefore, the overall unit performance may not be affected, and the protective effect may be considered to occur as needed to prevent more gradual degradation effects.

[0029] According to an embodiment, FIG. 5A to FIG. 5CAs shown in , when the reserve material 550 of the lithium-ion battery 500 is cast as a covering layer on the anode 530, the reserve material 550 can provide a "global" protection function, that is, the reserve material 550 is activated at any time when the potential at the surface of the anode 530 reaches the reaction potential of the reserve material 550. The lithium-ion battery 500 includes a cathode 510, a separator 520 and an anode 530. The anode 530 includes but is not limited to a main active material such as graphite, a conductive material and a binder. The conductive material can be but is not limited to conductive carbon, such as amorphous carbon. The binder can be but is not limited to a polymer binder. The anode 530 also includes a reserve active material or reserve material 550 laminated on the surface interface of the anode 530 between the separator 520 and the anode 530. As Figure 5B As shown in , when the reserve material 550 reacts with lithium, the lithiated reserve material 540 may undergo a volume change. Figure 5C As shown in , the start of the reaction at one location on the reserve material 550 layer can significantly increase the resistance of the cell not only at that location but also in the adjacent areas immediately surrounding the starting location if the reaction between lithium and reserve material 550 results in a significant volume expansion 560. This will in turn create a local overpotential that will bring additional reserve material 550 into reaction conditions, resulting in higher resistance, causing the cell potential to reach a cutoff potential, which causes the entire cell to shut down and thus enhance safety.

[0030] Refer again Figure 2 In the embodiment depicted in , to manufacture the cell design, a graphite anode layer is first made by casting a slurry containing graphite, carbon, a polymer binder and a solvent on a copper foil. Then, a slurry containing a reserve material, carbon, a polymer binder and a solvent is cast on the pre-cast anode layer. The bilayer anode is dried, calendered and combined with other battery components to form a cell. The thickness and amount of the reserve material will depend on the type of reserve material and the cell design. For example, if a reserve material with a capacity much higher than that of graphite is used, a thin reserve layer may be sufficient to provide the desired protection. Again referring to FIG. 4A to FIG. 4B In the embodiment depicted in , the reserve material can be integrated into the anode by mixing the reserve material directly with the anode components during the slurry manufacturing process. First, a slurry containing graphite, reserve material, conductive carbon, polymer binder and solvent is cast on copper foil. The casting is then dried, calendered and combined with other battery components to form a unit.

[0031] The N / P ratio of a lithium-ion cell is the ratio of the capacity of the anode (or negative electrode) to the capacity of the cathode (or positive electrode). In order to avoid lithium plating at the anode during charging, the capacity of the anode is generally higher than the capacity of the cathode. The use of reserve materials in the anode to inhibit lithium plating can also cause the N / P ratio of the anode capacity to the cathode capacity to decrease, thereby reducing costs and increasing unit energy. The reserve active material can have a significantly higher specific capacity or volumetric capacity than the main active material of the anode, so that the amount of reserve material is less than the amount of the main material required to prevent the voltage limit of lithium plating from being reached. Therefore, when compared to a conventional cell without a reserve active material, the amount of the main active material can be closer to a load approximately corresponding to N / P=1, thereby improving weight, volume and cost.

[0032] like Figure 6 As shown in , the N / P ratio is plotted for potential (V) versus state of charge (%, of the primary active material). When N / P is less than 1 (N / P<1), lithium will be plated on the anode when the cell is charged to 100% SOC because the potential will drop below the potential of the primary active material before reaching 100% SOC. When N / P=1, when the battery exceeds 100% SOC, the potential of the primary active material at 100% SOC will still drop and cause lithium plating, as previously described, due to low temperatures or high charging rates. When the N / P ratio is greater than 1 (N / P>1), the SOC of the primary active material exceeds 100%, and the potential will remain at the insertion potential of the primary active material, because there is 10% excess primary active material available for insertion, so lithium metal plating on the anode will not occur.

[0033] Fig. 7A and Figure 7B A graph of potential versus state of charge for different types of active materials is shown in accordance with an embodiment. Fig. 7A The SOC (SOC PAM ) potential (V). As the cell reaches 100% SOC of the primary active material, the active material "stages" at each potential. The reaction potential of the reserve material with lithium is also shown in the figure and is constant. When the cell reaches 100% SOC, the potential drops and remains at the reaction potential of the reserve material until the reserve material is fully intercalated, rather than the potential dropping to zero and causing lithium plating. In the case where the anode contains the primary active material and the reserve active material, the effective anode capacity is the sum of the capacity of the primary material and the capacity of the reserve material, thus making the anode have N eff / P is 1+δ(N eff / P=1+δ), where δ represents the capacity of the reserve material. Figure 7BA primary active material with a range of lithium solubility (solid solution) is depicted, so that the potential is stepped down (rather than staged in potential voltage). When the primary active material reaches 100% SOC, the potential drops to the potential of the reserve active material, delaying lithium plating on the anode until the reserve material is fully intercalated.

[0034] According to one or more embodiments, the reserve material may have a theoretical potential above the reaction potential of the primary material, but will not intercalate lithium at that potential due to its overpotential. Instead, the reserve material may intercalate lithium at a potential between the primary material reaction potential and the lithium reaction potential. This mechanism is shown in Figure 8 Where “D” represents the difference between the theoretical potential of the reserve active material and the overpotential of the reserve active material.

[0035] Thus, a lithium ion battery including an anode having a reserve active material is disclosed. The reserve material provides an active additional "reserve" material mixed within or layered on the anode that is activated only when the potential of the cell drops below that of the primary active material (when in a state where the primary active material is fully intercalated), such that lithium is intercalated with the reserve material rather than plated on the anode. Although typical additives for the anode include an active material for improving the capacity of the cell, the material is activated at the same time or before the graphite is intercalated, so conventional cells still have the problem of lithium plating on the anode.

[0036] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Instead, the words used in the specification are descriptive rather than restrictive, and it should be understood that various changes may be made without departing from the spirit and scope of the invention. In addition, the features of various implementation embodiments may be combined to form more embodiments of the invention.

Claims

1. A lithium ion battery, comprising: cathode; an anode having a main active material, conductive carbon, a binder and a reserve material; as well as The separator is located between the cathode and the anode. wherein the reserve material has a reaction potential between a lithium reaction potential and a main active material reaction potential, and the reserve material is configured to, in response to the main active material being completely intercalated with lithium at a 100% state of charge and the anode potential dropping to the reaction potential, intercalate the reserve material with lithium at the reaction potential to inhibit lithium plating on the anode, The reaction potential of the reserve material is between 0 volts and 0.1 volts. Among them, the reserve materials are SrO, Mn4N, K2SO4, CaCl2, CaF2, SrF2 or Mg.

2. The lithium ion battery according to claim 1, wherein The main active material includes graphite.

3. The lithium ion battery according to claim 1, wherein The reaction potential of the stock material is between 0.005 volts and 0.1 volts.

4. The lithium ion battery according to claim 1, wherein The capacity of the cathode is less than the sum of the capacity of the main active material of the anode and the capacity of the reserve material.

5. The lithium ion battery according to claim 1, wherein The reserve material irreversibly intercalates or deintercalates lithium.

6. The lithium ion battery according to claim 1, wherein: The reserve material reversibly intercalates or deintercalates lithium.

7. The lithium ion battery according to claim 1, wherein: The stock material is mixed with the main active material, conductive carbon and a binder.

8. The lithium ion battery according to claim 1, wherein: The reserve material forms a layer on the surface of the anode between the anode and the separator.

9. A method of operating a lithium ion battery, the method comprising: In response to the main active material in the anode of the battery being completely intercalated with lithium at a 100% state of charge and the anode potential of the battery dropping below the main active material potential, intercalating lithium into an anode reserve material having a reaction potential between the lithium reaction potential and the main active material potential to inhibit lithium plating on the anode, The reaction potential of the anode reserve material is between 0 volts and 0.1 volts. Among them, the anode reserve material is SrO, Mn4N, K2SO4, CaCl2, CaF2, SrF2 or Mg.

10. The method according to claim 9, wherein: The main active material includes graphite.

11. The method according to claim 9, wherein: The anode includes an anode reserve material mixed with a main active material, conductive carbon, and a polymer binder.

12. The method according to claim 9, wherein: The anode reserve material forms a layer disposed on the surface of the anode between the anode and the separator.

13. The method according to claim 9, wherein: The capacity of the cathode of the battery is less than the sum of the capacity of the main active material of the anode and the capacity of the anode reserve material.

14. The method according to claim 9, wherein: The reaction potential of the anode reserve material is between 0.005 volts and 0.1 volts.

15. The method according to claim 9, wherein: The anode reserve material reversibly intercalates and deintercalates lithium.

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