CN116018698A - A kind of electrode structure and the method for manufacturing this electrode structure - Google Patents

Abstract

An electrode structure for an alkali metal ion battery is described. The electrode structure includes a solid electrolyte capable of supporting alkali metal ions; an electrode adjacent to the solid electrolyte and an electrode current collector adjacent to the electrode capable of being in a first state wherein the electrode has a first alkali metal ion content and wherein The electrode transitions between a second state having a second alkali metal ion content higher than the first alkali metal content. In the first state, the electrode comprises: a first electrode layer comprising a first material capable of alloying with an alkali metal adjacent to the electrolyte, the first material having a first alkali metal ion content _A . In the second state, the electrode comprises: a first electrode layer comprising an alloy of a first material and an alkali metal having a second alkali metal ion content _A2 higher than the first alkali metal ion content _A1 , and at The second electrode layer between the first electrode layer and the electrode collector, the second electrode layer includes an alkali metal.

Description

A kind of electrode structure and the method for manufacturing this electrode structure

technical field

The present invention relates to electrode structures for alkali metal ion batteries, batteries comprising such electrode structures and methods of making such electrode structures.

Background technique

A solid battery structure typically includes an anode layer and a cathode layer separated by a solid electrolyte. The solid electrolyte contains alkali metal ions, such as lithium ions, and the alkali metal ions migrate between the anode and the cathode through the solid electrolyte when the battery is charged and discharged. Current collectors can be used for each of the anode and cathode to collect and conduct electrical current to appropriate points within the battery. The current collector is usually made of a conductive material such as a transition metal, and is usually provided in the form of a foil that is placed over and in electrical contact with the electrodes.

The anode may consist, for example, of an alkali metal layer. In this case, during charging of the battery, alkali metal ions from the electrolyte increase the volume of the alkali metal anode.

However, alkali metals are highly active materials that are difficult to handle. Therefore, making electrodes containing alkali metals is difficult, dangerous and expensive.

It would be desirable to produce a battery that avoids one or more of the problems associated with known battery structures.

Contents of the invention

Against this background, the present invention relates to an electrode structure for an alkali metal ion battery comprising: a solid electrolyte capable of carrying alkali metal ions; an electrode adjacent to the solid electrolyte and an electrode current collector adjacent to the electrode , the electrode is switchable between a first state in which the electrode has a first alkali metal ion content and a second state in which the electrode has a second alkali metal ion content higher than the first alkali metal content. In the first state, the electrode comprises a first electrode layer comprising a first material capable of alloying with an alkali metal adjacent to the electrolyte, the first material having a first alkali metal ion content A ₁ ; and in the In the second state, the electrode includes a first electrode layer and a second electrode layer, the first electrode layer includes an alloy of a first material and an alkali metal, the alloy has a second alkali metal ion content higher than the first alkali metal ion content A ₁ A ₂ , the second electrode layer is located between the first electrode layer and the electrode collector, and the second electrode layer includes alkali metal.

Forming a plating layer of alkali metal at the boundary between the first electrode layer and the electrode current collector layer is a particularly advantageous way of forming the alkali metal layer. The first electrode layer acts as a "buffer" controlling the rate of formation of the alkali metal layer. Because the first electrode material is alloyed with the alkali metal, in order to reach the boundary, the alkali metal ions not only need to diffuse through the first anodic layer, but also need to alloy with the material in the layer, which significantly slows down the kinetics of the plating process, while the thermodynamic Stablize. The slower growth rate of the plated layer provides a uniform alkali metal layer, avoiding dendrite growth, which results in uniform plating, improving the efficiency and performance of the electrode.

When the crystal structure, especially the crystal system, of the first electrode material is formed, it can be considered that the transformation between the first electrode material and the second electrode material caused by the alloying mechanism takes effect. This can also be expressed as a change in the space group or point group. Therefore, the first electrode material and the second electrode material differ in that they have different crystal systems, space groups or point groups.

The electrode can be an anode. The described electrode structures are particularly suitable for anode structures to be incorporated into electrochemical cells. When the electrode is an anode, the first state may correspond to a "discharged" (or partially discharged) state, and the second state may correspond to a "charged" (or partially charged) state.

The first electrode material is preferably selected from: tin, tin germanium, bismuth, silver, aluminum, zinc, germanium or lithium phosphide. The material is safe, effective, and relatively easy to manufacture, for example using physical vapor deposition (PVD) techniques.

The first electrode layer may be a PVD deposited layer. PVD is a particularly convenient method for producing battery structures, especially for producing layered structures.

The electrode current collector preferably includes a deposition layer deposited on the electrode. This provides an intimate contact between the electrode collector and the electrode, maximizing the efficiency and effectiveness of the electrode collector layer, minimizing losses, and also allowing the electrode collector layer to provide particularly effective protection against the passage of alkali metals through the electrode surface loss in response.

The electrode current collector layer can resist alloying with alkali metals. In this way, the alkali metal will not be carried into the current collector layer, where it will no longer contribute to the capacity of the battery, but will remain in the first and second anode layers. This also prevents loss of alkali metal through the electrode current collector layer. Preferably, the electrode current collector layer comprises a transition metal, most preferably selected from: copper, platinum, nickel, molybdenum and tungsten. These materials are effective current collector layers that are easy to produce.

In the first state, the electrode may include a second electrode layer between the first electrode layer and the electrode collector, the second electrode layer including an alkali metal. The thickness of the second layer in the first state may be greater than in the second state. In this case, some portion of the second electrode layer (ie, the alkali metal layer) remains in the first state. This may be due to parasitic losses where a certain amount of second layer is always left. Alternatively, this may be because the first state is a state in which only a portion of the alkali metal content has been removed from the electrode (eg by charging or discharging of the electrode), so that some alkali metal layer remains. In this case, further removal of alkali metal ions can take place at a future point, if desired, in which case the alkali metal layer can be removed.

In the first state, the alkali metal content _A1 of the first electrode material may be less than 1 at%, preferably substantially 0 at%. In other words, in the first state, the first electrode layer may be substantially free of alkali metal ions in the first state. This is advantageous because it maximizes the capacity of the electrodes, and thus the capacity of the battery into which the electrodes are incorporated.

Alkali metals may be, for example, lithium and/or sodium. Lithium and sodium are particularly preferred because they are light but highly reactive, thus providing high energy density batteries. Sodium and lithium also intercalate favorably. Lithium may be particularly preferred in some cases because of its particularly high energy density. In other cases sodium may be particularly preferred as it is a less reactive and therefore less hazardous material that is easier to handle.

The invention also extends to an alkali metal ion battery comprising the electrode structure described above and a further electrode adjacent to a solid electrolyte. In case the electrode is an anode, the other electrode may be a cathode. In this way, the electrodes can be incorporated into batteries that can be used to power devices.

The first electrode layer may have a first alkali metal ion inventory I ₁ determined by the first electrode material and/or the thickness of the first electrode layer. The further electrode may have a second alkali metal ion inventory I ₂ determined by the further electrode material and/or the thickness of the further electrode layer. I ₁ and I ₂ can be chosen such that I ₁ ≦0.5I ₂ . In this way, the alkali metal ion inventory of the first electrode layer is less than or equal to half of the alkali metal ion inventory of the other electrode. This means that when all alkali metal ions have been transferred from said other electrode to said electrode, at most half of the stock of alkali metal ions is occupied by the first electrode layer and thus by the alloying mechanism, and at least half of the alkali metal The ion inventory can be used to form the second electrode layer, the alkali metal layer. Ensuring that at least half of the alkali metal inventory is available for the alkali metal layer provides high battery capacity since greater capacity can be achieved by electroplating alkali metal than by alloying mechanisms.

The invention further extends to a method of making an electrode structure for an alkali metal ion battery, the method comprising: providing a solid electrolyte layer comprising alkali metal ions; depositing an electrode on the solid electrolyte layer, the electrode comprising a first electrode layer, a first The electrode layer includes a first electrode material capable of alloying with an alkali metal; and an electrode current collector layer is deposited on the electrode. This provides a convenient and efficient method of fabricating the electrode structures described above.

The method may include depositing an electrode layer and/or an electrode current collector layer using a physical vapor deposition method. PVD is a particularly convenient method for producing battery structures, especially for producing layered structures.

The method can include rendering the electrode structure substantially free of alkali metals. This advantageously allows the fabrication of electrodes without the need to form any alkali metal layers or features, which would otherwise be relatively expensive and dangerous. Such a state substantially free of alkali metals may correspond to, for example, a discharged state, which may be a less hazardous state for the manufacture of the electrode and may allow the electrode to be handled and sold without the need for an additional discharge step .

The present invention also includes an electrode structure for an alkali metal ion battery, the electrode structure comprising: a solid electrolyte capable of carrying alkali metal ions; an electrode adjacent to the solid electrolyte and an electrode collector adjacent to the electrode, the electrode Switchable between a first state in which the electrode has a first alkali metal ion content and a second state in which the electrode has a second alkali metal ion content higher than the first alkali metal content. The electrode comprises a first electrode layer adjacent to the solid electrolyte, the first electrode layer comprising an alloy of a first electrode material and an alkali metal; and a second electrode layer positioned between the first electrode layer and an electrode current collector, the second electrode layer comprising alkali metal. In the first state the second electrode layer has a thickness t ₁ and in the second state the second electrode layer has a thickness t ₂ which is greater than t ₁ .

Forming a plating layer of alkali metal at the boundary between the first electrode layer and the electrode current collector layer is a particularly advantageous way of forming the alkali metal layer. The first electrode layer acts as a "buffer" controlling the rate of formation of the alkali metal layer. Because the first electrode material is alloyed with the alkali metal, in order to reach the boundary, the alkali metal ions not only need to diffuse through the first anodic layer, but also need to alloy with the material in the layer, which significantly slows down the kinetics of the plating process, while the thermodynamic Stablize. The slower growth rate of the plated layer provides a uniform alkali metal layer, avoiding dendrite growth, which results in uniform plating, improving the efficiency and performance of the electrode.

When the crystal structure, in particular the crystal system, of the first electrode material is formed, it can be considered that the transformation between the first electrode material and the second electrode material caused by the alloying mechanism takes effect. This can also be expressed as a change in the space group or point group. Therefore, the first electrode material and the second electrode material differ in that they have different crystal systems, space groups or point groups.

The electrode can be an anode. The described electrode structures are particularly suitable for anode structures to be incorporated into electrochemical cells. When the electrode is an anode, the first state may correspond to a "discharged" (or partially discharged) state, and the second state may correspond to a "charged" (or partially charged) state.

The first electrode material is preferably selected from: tin, tin germanium, bismuth, silver, aluminum, zinc, germanium or lithium phosphide. The material is safe, effective, and relatively easy to manufacture, for example using physical vapor deposition (PVD) techniques.

The first electrode layer may be a PVD deposited layer. PVD is a particularly convenient method for producing battery structures, especially for producing layered structures.

The electrode current collector preferably includes a deposition layer deposited on the electrode. This provides an intimate contact between the electrode collector and the electrode, maximizing the efficiency and effectiveness of the electrode collector layer, minimizing losses, and also allowing the electrode collector layer to provide particularly effective protection against the passage of alkali metals through the electrode surface loss in response.

The electrode current collector layer can resist alloying with alkali metals. In this way, the alkali metal will not be carried into the current collector layer, where it will no longer contribute to the capacity of the battery, but will remain in the first and second anode layers. This also prevents loss of alkali metal through the electrode current collector layer. Preferably, the electrode current collector layer comprises a transition metal, most preferably selected from: copper, platinum, nickel, molybdenum and tungsten. These materials are effective current collector layers that are easy to produce.

Solid electrodes may contain alkali metal ions.

Alkali metals may be, for example, lithium and/or sodium. Lithium and sodium are particularly preferred because they are light but highly reactive, thus providing high energy density batteries. Sodium and lithium also intercalate favorably. Lithium may be particularly preferred in some cases because of its particularly high energy density. In other cases sodium may be particularly preferred as it is a less reactive and therefore less hazardous material that is easier to handle.

The invention also extends to an alkali metal ion battery comprising the electrode structure described above and a further electrode adjacent to a solid electrolyte. In case the electrode is an anode, the other electrode may be a cathode. In this way, the electrodes can be incorporated into batteries that can be used to power devices.

The invention also extends to a method of making an electrode structure for an alkali metal ion battery, the method comprising: providing a solid electrolyte layer comprising alkali metal ions; depositing a first electrode layer on the solid electrolyte layer, the first electrode layer comprising i) a first electrode material capable of alloying with an alkali metal or ii) an alloy of an alkali metal and the first electrode material; depositing a second electrode layer on the first electrode layer, the second electrode layer comprising an alkali metal layer; and depositing on the second electrode An electrode current collector layer comprising a material resistant to alloying with an alkali metal is deposited on the layer. This method provides a facile method for fabricating the electrodes described above.

The method may include depositing an electrode layer and/or an electrode current collector layer using a physical vapor deposition method. PVD is a particularly convenient method for producing battery structures, especially for producing layered structures.

The method may include placing the electrode structure in a first state. This advantageously allows the fabrication of electrodes with a relatively low content of alkali metal ions. This may correspond to, for example, a discharge state, which may be a less hazardous state for the manufacture of the electrode and may allow handling and sale of the electrode without the need for an additional discharge step.

In embodiments where the first electrode layer comprises i) a first electrode material capable of alloying with an alkali metal, the method may further comprise the step of increasing the alkali metal ion content of the electrode, thereby alloying the first electrode material with an alkali metal to form the second electrode material. This advantageously allows the electrode to be fabricated initially when the first electrode layer is in an unalloyed state, which may be easier than fabricating the layer in an alloyed state, and allows the first electrode layer to undergo a subsequent alloying process. The step of increasing the alkali metal ion content of the electrode may include charging the electrode.

The features of any one aspect or embodiment above can also be applied independently or in proper combination to the features of other aspects and embodiments.

Description of drawings

For easier understanding of the invention, embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

1 is a schematic diagram of a battery according to a first embodiment in a discharged state;

Figure 2 is a schematic diagram of the battery of Figure 1 in a charged state;

Figures 3a to 3c are schematic illustrations of stages in a method of manufacturing the battery of Figure 1;

Figure 4 is a schematic diagram of a battery according to a second embodiment in a discharged state;

Figure 5 is a schematic diagram of the battery of Figure 4 in a charged state;

Figure 6 is a schematic illustration of the battery of Figures 4 and 5 in an alternate state of discharge at its point of manufacture; and

7a to 7c are schematic diagrams of stages in a method of manufacturing the battery of FIG. 6 .

Detailed ways

Figures 1 and 2 illustrate a battery 10 for an alkali metal ion battery such as a lithium ion battery or a sodium ion battery.

The battery includes two electrodes: a first electrode, referred to herein as the anode 14 , and another or second electrode, referred to herein as the cathode 12 . The electrodes 12 , 14 are separated by a solid electrolyte 16 . Solid electrolyte 16 is made of a material in which alkali metal ions are diffusible so that the alkali metal ions can move back and forth between anode 14 and cathode 12 for charging and discharging of battery 10 . A solid electrolyte may be any suitable solid or semi-solid material, such as ion-conducting polymers, ceramics, gels, or materials comprising a solid or semi-solid matrix material.

An anode current collector layer 22 is on the anode 14 . In this example, anode current collector layer 22 is deposited directly on anode 14 such that it is in intimate contact with anode 14 .

Anode 14 is switchable between a first state, in which anode 14 has a relatively low alkali metal ion content, and a second state, referred to herein as a discharge state and shown in FIG. , the anode 14 has a relatively high alkali metal ion content, referred to herein as the state of charge and shown in FIG. 2 . In this case, Figure 1 shows a fully discharged state and Figure 2 shows a fully charged state, although it should be understood that the anode could also be in a partially charged state. Where the alkali metal is lithium, the first or discharged state may also be referred to as the delithiated state and the second or charged state may also be referred to as the lithiated state.

In a discharged state, anode 14 includes a first anode layer 24 adjacent to electrolyte 16 . The first anode layer 24 includes a first material 26 capable of forming an alloy with the alkali metal of the cell. The first material 26 has a first alkali metal ion content A ₁ .

In a charged state, anode 14 includes a first anode layer 24 adjacent electrolyte 16 and a second anode layer 28 positioned between first anode layer 24 and anode current collector layer 22 . In this charged state, the first anode layer 24 comprises a second material 29 different from the first material 26 , in particular an alloy of the first material 26 and an alkali metal. The second material 29 has a second alkali metal ion content _A2 that is higher than the first alkali metal ion content _A1 .

The second anode layer 28 includes an alkali metal.

As will be explained in more detail below, battery 10 may advantageously be fabricated in the discharged state of FIG. 1 , wherein anode 14 is substantially free of alkali metals. In this state, the anode 14 includes only the first anode layer 24 with an alkali metal ion content A ₁ of substantially zero. In other words, first anode layer 24 is substantially free of alkali metals, but is capable of alloying with alkali metals.

When the battery is charging, the anode undergoes two mechanisms of anode charging. These mechanisms are described here sequentially, but it should be understood that these mechanisms may occur in parallel to some extent.

The first anodic charging mechanism is the alloying mechanism. Through this mechanism, alkali metal ions diffuse from the electrolyte 16 into the first anode layer 24 and alloy with the first material 26 . Eventually, when enough alkali metal ions have diffused into the first anode layer 24, the first anode material 26 will have been sufficiently alloyed with the alkali metal ions, and the first anodic layer 24 will be saturated with alkali metal ions. In this state, the first anodic layer 24 will now comprise a second anodic material 29 which is an alloy of the first anodic material 26 and an alkali metal.

The difference between the second anode material 29 and the first anode material is that the alkali metal ion content A ₂ of the second anode material 29 is greater than the first alkali metal ion content A ₁ of the first anode material. The difference of the second anode material 29 also lies in that the alloyed second anode material has different crystal structures, especially different crystal systems. As a non-limiting example, the crystal system of the first anode material 26 may be cubic and the crystal system of the second anode material 29 may be trigonal. In other words, the space group or point group of the alloy material varies between the first material 26 and the second material 29 . Thus, a transition between the first and second anode materials 26, 29 can be said to occur when the crystal system, space group or point group of the material is changed. This alloying mechanism is particularly advantageous because it is thermodynamically stable.

The second anodic charging mechanism is the alkali metal plating mechanism. As charging continues, more alkali metal ions diffuse into the first anode layer 24 . However, once the first anode layer 24 is saturated with alkali metal ions, these ions can no longer be accommodated in the first anode layer 24 . Instead, the alkali metal ions will diffuse to the boundary 30 between the first anode layer 24 and the current collector layer 22 . The material of the current collector layer 22 is selected such that it is resistant to alloying with alkali metals and resistant to diffusion of alkali metal ions. Thus, the alkali metal will be “plated” at the boundary 30 between the first anode layer 24 and the current collector layer 22 . This electroplating forms a second anode layer 28 comprising an alkali metal.

Charging is complete when substantially the entire inventory of alkali metal ions at the cathode has been transferred to the anode (either as part of the alloy of the first anode layer 24 or as part of the plated alkali metal of the second anode layer 28). In this state, the battery is ready for discharge.

During discharge, reverse anode mechanisms will occur: specifically, i) a dealloying mechanism by which alkali metal ions will diffuse out of the first anode layer 24 to the solid electrolyte 16, eventually dealloying the second material 29 Returning to the first material 26 , and ii) the deplating mechanism by which the alkali metal of the second anode layer 28 diffuses back through the first anode layer 24 to the solid electrolyte 16 . This reduces the thickness of the second anode layer 28 from the thickness t ₂ in the charged state to the thickness t ₁ in the discharged state. In this example, the thickness t ₁ is substantially zero.

Forming an alkali metal plating layer at the boundary 30 between the first anode layer 24 and the anode current collector layer 22 is a particularly advantageous way of forming the alkali metal layer 28 . The first anode layer 24 acts as a "buffer" that controls the rate of formation of the alkali metal layer 28 . In particular, in order to reach the boundary 30, the alkali metal ions not only need to diffuse through the first anodic layer, but also alloy with the material in this layer, which significantly slows down the kinetics of the electroplating process. The slower growth rate of the electroplated layer provides a uniform alkali metal layer that avoids dendrite growth. This is particularly advantageous because otherwise the dendrites would "block" the surface area of the electrolyte, preventing diffusion and reducing the efficiency of the plating process and thus the efficiency of the electrode. Dendrites also have a higher surface energy than the surrounding surface, so that when dendrites are present, plating occurs preferentially on the dendrites, resulting in an inhomogeneous layer. Therefore, the absence of dendrites improves the efficiency and performance of the cell.

Consider the anode layer in more detail:

The first material 26 of the first anode layer 24 is selected to be capable of alloying with an alkali metal. Therefore, the properties of the first material depend on the alkali metal of the cell. Suitable materials include, for example: silicon (Si), tin (Sn), germanium (Ge), lead (Pb), arsenic (As), indium (In), gold (Au), silver (Ag), cadmium (Cd) , aluminum (Al), zinc (Zn), bismuth (Bi), bismuth-containing compounds, lithium phosphate (Li _x P), tin, germanium or silicon-based alloys (Sn-M, Ge-M, Si-M, where M are G2-G7 atoms), transition metal-based compounds (such as Tm-P, TmSby _y , Tm-Zn, where Tm is a transition metal), and conductive transition metal oxides (such as F _x O _y , NiO, CoO, MnO ₂ , Cr ₂ O ₃ , CuO).

Particularly preferred materials that may be particularly suitable for lithium-ion batteries include, for example: tin (Sn), Sn-M (wherein M is a G2-G7 atom), _TmSby (wherein Tm is a transition metal), bismuth (Bi), silver ( Ag), aluminum (Al) and zinc (Zn). In these cases, the second material 29 of the first anode layer 24 will accordingly be (wherein AM represents an alkali metal), a Sn-AM alloy, a Sn-M-AM alloy (wherein M is a G2-G7 atom), TmSb _y - AM alloys (where Tm is a transition metal), Bi-AM alloys, Ag-AM alloys, Al-AM alloys or Zn-AM alloys.

The first anodic layer will have a capacity of a first alkali metal ion inventory I ₁ determined by the first anode material and/or the thickness of the first anodic layer. When the first anode layer is fully alloyed so that it is saturated with alkali metal ions, and the second anode material has been formed, this inventory _I1 will be completely contained in the first anode layer.

The first anode material is preferably chosen such that it forms an alloy with the alkali metal having a relatively low alkali metal inventory I ₁ , ie it has a relatively low alkali metal content A ₂ when the alloy is saturated with the alkali metal. Selecting a relatively low alkali metal inventory means that relatively less alkali metal is included in the alloy of the second anode material and more alkali metal is available for the Alkali metal is plated at the boundary 30 . By ensuring that a large amount of alkali metal is available for the plating mechanism, the capacity of the battery can be maximized.

When an anode 14 is incorporated into a battery 10 with a cathode 12, as shown in Figures 1 and 2, the cathode will have a second inventory of alkali metal ions _I2 determined by the cathode material and/or the thickness of the cathode layer. The parameters of the first anode layer (in particular, the first anode material and the thickness of the first anode layer) are preferably chosen specifically such that I ₁ ≦0.5I ₂ . This means that when the cathode's inventory is discharged by 50% or less, the first anode layer will be saturated with alkali metal ions. The remaining inventory (I ₂ −I ₁ ) of cathode 12 will then be accommodated in second anode layer 26 as a soda alkali metal.

Although a relatively low alkali metal inventory _I is desirable for the first anode layer 24, it should be noted that since the second anode material 29 is an alloy mixture of an alkali metal and the first alloy material 26 (rather than, for example, some small amount of alkali metal ions non-alloyed materials that may diffuse through), so the alkali metal content of the alloy will still be high enough to form the alloy. For example, the alkali metal ion content of the second anode material may be at least 10 at%, preferably at least 20 at%.

The first material is deposited directly onto the solid electrolyte, preferably by physical vapor deposition.

The thickness of the first material layer is tailored to the requirements of the battery and can be influenced by factors including the cathode inventory as described above, and also by the choice of electrolyte and first anode material. Typical thicknesses will, for example, be between about 5 nanometers and about 100 micrometers, depending on the parameters and materials of the electrodes and the battery into which they are incorporated. In general, it is desirable that the first layer of material is as thin as possible. A particularly preferred thickness is one capable of providing an excess capacity of about 20% of the lithium inventory of the cathode.

The material of the anode current collector layer is chosen to be resistant to alloying with alkali metals and to resist diffusion of alkali metals through the layer. This ensures that the alkali metal will be plated at the boundary between the first anode layer and the current collector layer, rather than alloyed with or diffused through the current collector layer, which would otherwise allow alkali metal ions to escape, depleting the The capacity of the battery. The material of the anode current collector layer is also selected to be conductive.

Suitable materials for the anode current collector include transition metals that resist alloying with the cell's alkali metal ions: eg copper (Cu), platinum (Pt), nickel (Ni), molybdenum (Mo) and tungsten (W).

The solid electrolyte can be any suitable material capable of supporting alkali metal ions. For example, when the alkali metal of the battery is lithium, the solid electrolyte may be LiPON.

The anode can be fabricated using the physical vapor deposition (PVD) method which will now be described with reference to Figures 3a to 3c.

Preferably, the anode 14 is brought into the uncharged state shown in FIG. 1 . Leaving the anode 14 in an uncharged state is particularly advantageous because in this state the anode 14 is substantially free of highly reactive alkali metals, making it easier to manufacture and handle. There is no need to deposit any soda metal layers, which facilitates fabrication.

As shown in Figure 3a, a solid electrolyte 16 is first provided. In the example of Figure 3a, the solid electrolyte 16 is the top layer of a structure that also includes a cathode layer and a cathode current collector. Solid electrolyte 16 defines the substrate on which anode 14 will subsequently be deposited.

Next, as shown in FIG. 3 n , a first anode layer 24 comprising a first anode material 26 is deposited onto the solid electrolyte 16 . Materials are deposited using PVD methods, such as sputtering. Therefore, the solid electrode 16 is arranged in the vacuum chamber of the sputtering device prior to deposition.

With the first anode layer 24 in place, the anode current collector layer 22 is deposited on the first anode layer 24 . The first anode current collector layer 22 is also deposited using a PVD method, such as sputtering.

In this example, there is no need to deposit any additional anode layer prior to the anode current collector layer 22 . In particular, there is no need to deposit a second anode layer comprising an alkali metal, since this layer can be formed during the subsequent charging process.

With the anode current collector layer 22 in place, the anode 14 is intact in its uncharged state and can be removed from the deposition apparatus. The anode is then ready for use in the battery, where it can be charged and discharged according to the mechanisms described above.

The described anode structure provides a high energy density battery that can be fabricated exclusively in the discharged state, allowing safe and easy fabrication. Because the primary anode charging mechanism is the plating of alkali metals, the battery has a high capacity. Electroplating the alkali metal under the deposited current collector layer means that the alkali metal is not lost from the battery and the capacity is maintained. The presence of the alloy material means that lithium plating occurs at a low rate, promoting uniform plating and reducing dendrite growth, which would otherwise hinder battery capacity.

Another embodiment of the invention will now be described with reference to Figures 4, 5, 6 and 7a to 7d.

Figures 4 and 5 show an anode 114 similar to the anode 14 of Figures 1 and 2, except that i) a second anode layer 128 comprising an alkali metal is present in both charge and discharge states, and ii) the first alloy layer 124 comprises Second material 129 in both charge and discharge states. In this embodiment, the overall volume and thus overall thickness of the second anode layer 128 is greater in the charged state than in the discharged state.

Referring to FIG. 4 illustrating a discharged state, in the discharged state, the anode 114 includes a first anode layer 124 adjacent to the electrolyte 116 and a second anode layer 128 between the first anode layer 124 and the anode current collector layer 122 . In this embodiment, the first anode layer 124 includes a second material 129 that is an alloy including the alkali metal of the cell, having an alkali metal ion content _A2 . The second anode layer 128 includes an alkali metal and has a first thickness t ₁ .

In the state of charge shown in FIG. 5 , the anode 114 includes a first anode layer 124 adjacent to the electrolyte 116 and a second anode layer 128 positioned between the first anode layer 124 and the anode current collector layer 122 . In this charged state, the first anode layer 124 also includes the second material 129 . The second anode layer 128 includes an alkali metal and has a second thickness t ₂ greater than the first thickness t ₁ .

Like the anodes of Figures 1 and 2, the anodes of Figures 4 and 5 can be fabricated in a discharged state. In this case, however, the anode is not produced in exactly the discharge state of FIG. 4 , but in an alternative discharge state shown in FIG. 6 . This state is substantially the same as the discharge state of FIG. 4, except that the first anode layer 124 comprises the same type of first material 126 as in the embodiment of _FIG . Alkali metal ion content A ₁ , in this case A ₁ is essentially zero.

When the battery is charged for the first time after manufacture, the anode is charged from the alternate discharge state of FIG. 6 to the charge state of FIG. 5 . The anode undergoes the same two anodic charging mechanisms as the anodes of Figures 1 and 2: the alloying mechanism and the plating mechanism. The alloying mechanism is basically the same as above. The alkali metal plating mechanism is similar to that described above, but in this case some alkali metal is already present in the second anode layer 128 between the first anode layer 124 and the current collector layer 122 . In this case, the thickness of the alkali metal of the second anode layer 128 increases from an uncharged thickness t ₁ to a charged thickness t ₂ when the alkali metal is "plated" during charging. In this way, the overall volume of the alkali metal and thus the overall volume of the second anode layer 128 increases during charging by means of the electroplating mechanism.

During the first (and all subsequent) discharge cycles, the anode is discharged from the charged state of FIG. 5 to the discharged state of FIG. 4 . A deplating mechanism will occur by which at least some of the alkali metal of the second anode layer 128 diffuses through the first anode layer 124 back to the solid electrolyte 116 via an alloying mechanism such that the thickness of the second anode layer decreases from _t as small as t ₁ . In this embodiment, the discharge cycle does not involve dealloying of the first anode layer 124 .

During the subsequent charging cycle, the anode is charged from the discharged state of FIG. 4 to the charged state of FIG. 5 . During this charge cycle, the anode does not undergo an alloying mechanism, but only an alkali metal plating mechanism as described above, wherein the alkali metal thickness of the second anode layer 128 increases from an uncharged thickness t ₁ to a charged thickness t ₂ .

Subsequent charge and discharge cycles continue as described above, with the anode charging and discharging between the discharge state of FIG. 4 and the charge state of FIG. 5 . Since the first anode layer 124 has not undergone dealloying, the anode does not return to the alternate discharge state of FIG. 6 .

7a to 7d show various stages in the manufacture of the anode shown in FIG. 6 . The process is generally similar to that described in connection with Figures 3a to 3c, except that the alkali metal layer is deposited in an additional step.

As shown in Figure 7a, a solid electrolyte 116 is first provided. In the example of Figure 7a, the solid electrolyte 116 is the top layer of a structure that also includes a cathode layer and a cathode current collector. Solid electrolyte 116 defines the substrate upon which anode 114 will subsequently be deposited.

Next, as shown in FIG. 7 b , a first anode layer 124 comprising a first anode material 126 is deposited onto the solid electrolyte 116 . Materials are deposited using PVD methods, such as sputtering. Thus, the solid electrode 116 is arranged in the vacuum chamber of the sputtering apparatus prior to deposition.

With the first anode layer 124 in place, as shown in Figure 7c, a second anode layer 128 comprising an alkali metal is deposited on top of the first anode layer 124, also using PVD methods such as sputtering.

Next, as shown in FIG. 7 d , an anode current collector layer 122 is deposited on the second anode layer 128 . The anode current collector layer 122 is also deposited using a PVD method, such as sputtering.

With the anode current collector layer 122 in place, the anode is intact in its alternate discharge state and can be removed from the deposition apparatus. The anode is then ready for use in the battery, where it can be charged and discharged according to the mechanisms described above.

It should be understood that sublayers may be present in any of the anode layers described above. For example, the first anode layer may comprise sublayers of different materials, some or all of which may be alloyed with an alkali metal.

In the examples above, the anode structure has been described in fully charged and fully discharged states. However, it should be understood that the anode structure may also exist in a partially charged state. It should also be understood that, in practice, a battery may not be able to achieve full states of charge and discharge due to parasitic reactions and kinetic limitations within the battery. For example, in the first embodiment, dealloying may not be complete, so that in the discharged state, a small amount of alkali metal ions may remain in the first anode layer, such that _A1 may not be 0, but may be such as ≤ 1 at % smaller value of . Deplating may also be incomplete such that a small amount of the second anode layer exists in a discharged state.

Other variations will be apparent to the skilled person without departing from the scope of the appended claims.

Claims (15)

1. An electrode structure for an alkali metal ion battery, the electrode structure comprising:

a solid electrolyte capable of supporting alkali metal ions;

an electrode adjacent to the solid electrolyte and being switchable between a first state in which the electrode has a first alkali metal ion content and a second state in which the electrode has a second alkali metal ion content higher than the first alkali metal ion content;

an electrode current collector adjacent to the electrode;

the method is characterized in that:

in the first state, the electrode includes:

a first electrode layer comprising a first material capable of alloying with an alkali metal adjacent to the electrolyte, the first material having a first alkali metal ion content A ₁ The method comprises the steps of carrying out a first treatment on the surface of the And is also provided with

In the second state, the electrode includes:

a first electrode layer comprising an alloy of the first material and an alkali metal, the alloy having a higher content A of alkali metal ions than the first material ₁ Second alkali metal ion content A of (2) ₂ And (b)

And a second electrode layer between the first electrode layer and the electrode current collector, the second electrode layer including an alkali metal.

2. The electrode structure of claim 1, wherein the electrode is an anode.

3. The electrode structure of claim 1 or 2, wherein the first electrode material is selected from the group consisting of tin, tin-germanium, bismuth, silver, aluminum, zinc, germanium, or lithium phosphide.

4. The electrode structure of any preceding claim, wherein the first electrode layer is a PVD deposited layer.

5. An electrode structure as claimed in any preceding claim wherein the electrode current collector comprises a deposited layer deposited on the electrode.

6. An electrode structure according to any one of the preceding claims, wherein the electrode current collector layer is resistant to alloying with alkali metals and preferably comprises a transition metal, most preferably selected from the group consisting of copper, platinum, nickel, molybdenum and tungsten.

7. The electrode structure of any preceding claim, wherein in the first state the electrode comprises a second electrode layer between the first electrode layer and the electrode current collector, the second electrode layer comprising an alkali metal, and wherein the thickness of the second layer in the first state is greater than the thickness in the second state.

8. The electrode structure of any one of the preceding claims, wherein in the first state the alkali metal content a of the first electrode material ₁ Less than 1at%, preferably substantially 0at%.

9. The electrode structure of any preceding claim, wherein the alkali metal is lithium or sodium.

10. An alkali metal ion battery comprising an electrode structure according to any preceding claim and another electrode adjacent the solid electrolyte.

11. An alkali metal ion battery according to claim 10, wherein said other electrode is a cathode.

12. The alkali metal ion battery of claim 11, wherein the first electrode layer has a first alkali metal ion inventory I determined by the first electrode material and/or the thickness of the first electrode layer ₁ The other electrode has a second alkali metal ion stock I determined by the thickness of the other electrode material and/or the other electrode layer ₂ And wherein I ₁ ≤0.5I ₂ 。

13. A method of manufacturing an electrode structure for an alkali metal ion battery, the method comprising:

providing a solid electrolyte layer comprising alkali metal ions;

depositing an electrode on the solid electrolyte layer, the electrode comprising a first electrode layer comprising a first electrode material capable of alloying with an alkali metal; and

an electrode current collector layer is deposited on the electrode.

14. A method according to claim 13, comprising depositing the electrode layer and/or the electrode current collector layer using a physical vapour deposition method.

15. A method according to claim 13 or 14, comprising bringing the electrode structure into a substantially alkali metal free state.

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