3D porous mixed ionic-electronic conductor (MIEC) architecture for dimensionally stable all-solid-state batteries

Abstract

Described herein is a composite anode architecture for solid-state batteries comprising a mixed ion-electron conductor having a plurality of shells spaced from one another by gaps and having closed pores in the shells and open pores in the gaps; and a volume of β-phase disposed in the open pores and the closed pores. In some embodiments, the composite anode architecture for solid-state batteries further comprises an interconnection between the plurality of shells.

Description

3D POROUS MIXED IONIC-ELECTRONIC CONDUCTOR (MIEC) ARCHITECTURE FOR DIMENSIONALLY STABLE ALL-SOLID-STATE BATTERIESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. §119 of U.S. Provisional Patent Application No. 63 / 660,735 filed on June 17, 2024, which is hereby incorporated by reference herein in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] N / ABACKGROUND

[0003] All-solid-state batteries (ASSB), which refer to batteries with no liquid components, have garnered considerable attention due to their safety and energy density advantages, potentially enabling the deployment of advanced battery chemistries. Remarkable progress has been made in enhancing ASSB performance. However, a significant challenge that remains is ensuring the dimensional stability of these batteries regardless of their state of charge, particularly when using body-centered cubic alkali metals (such as lithium (Li), sodium (Na), potassium (K)) or their alloys with minor solute elements as anodes.SUMMARY OF DISCLOSED EMBODIMENTS

[0004] While three-dimensional (3D) open-porous structures have been successfully employed to address the changing thickness in liquid electrolyte-based batteries, the task is more complex in solid-state batteries due to the lack of fluidity in solid electrolytes. Since liquid electrolyte is fluidic, Li-ions can access the entire 3D open-porous structure even if the 3D open-porous structure does not conduct Li-ions, provided that the liquid electrolyte and the 3D open-porous structure have good wettability. In contrast, in solid-state batteries, if the 3D porous structure conducts only Li-ions or only electrons, lithium is often deposited on one side of the 3D porous layer rather than inside it.

[0005] A class of materials known as mixed ionic-electronic conductors (MIECs) have become notably useful in conjunction with the conventional use of a solidelectrolyte (SE) and metal (M) in batteries with their conducting properties making Li-ions and electrons accessible throughout the 3D porous layer. Such a mixed ionic-electronic conductor (MIEC) can possess a specific 3D architecture to effectively manage the mechanical stresses and chemical corrosiveness associated with the -phase. For example, a honeycomb-type structure can be utilized as a 3D architecture, with specific design guidelines for various design factors including the ratio between wall thickness and pore width.

[0006] p-phase refers to body-centered cubic alkali metals or their alloys with minor solute elements, such as silver (Ag), gold (Au), magnesium (Mg), etc., in a body-centered cubic crystal structure. One of the primary obstacles arises from the repetitive expansion and contraction of the p-phase during cycling, leading to variations in the overall stack thickness. The variations arise from the changing thickness of the anode, which contracts and expands during use, changing the overall thickness of the battery.

[0007] Disclosed here is a 3D MIEC architecture (which may be referred to herein as a composite anode architecture) designed for dimensionally stable electrodes in all-solid-state batteries (ASSBs). The disclosed architecture incorporates a combination of open and closed pores formed from various pore shells. The pore shells can be interconnected intrinsically or extrinsically.

[0008] According to one aspect of the disclosure, a composite anode architecture for solid-state batteries comprises a mixed ion-electron conductor having a plurality of shells spaced from one another by gaps and having closed pores in the shells and open pores in the gaps; and a volume of p-phase disposed in the open pores and the closed pores.

[0009] In some embodiments, the composite anode architecture for solid-state batteries further comprises an interconnection between the plurality of shells. In some embodiments, the composite anode architecture for solid-state batteries further comprises an interconnection between the plurality of shells and the plurality of shells are extrinsically interconnected using one dimensional (1 D) components, two dimensional (2D) components, or three dimensional (3D) components. In some embodiments, the composite anode architecture for solid- state batteries further comprises an interconnection between the plurality of shells and the plurality of shells are intrinsically interconnected through sintering.

[0010] In some embodiments, an areal porosity varies throughout the composite anode architecture compared to a volumetric porosity of the composite anode architecture. In some embodiments, the volume of p-phase is formed of at least one of lithium (Li), sodium (Na), or potassium (K). In some embodiments, the closed pores have a shortest cross-sectional width of less than 800 nm. In some embodiments, the closed pores have a shortest cross-sectional width less than 800 nm and the plurality of shells have a thickness of 2-30% of their cross- sectional width. In some embodiments, the volume of p-phase is at least 40% of a total volume of the composite anode architecture.

[0011] According to another aspect of the disclosure, an all-solid-state battery comprises a current collector; a composite anode architecture disposed on the current collector. In some embodiments, the composite anode architecture comprises a mixed ion-electron conductor having a plurality of shells spaced from one another by gaps and having closed pores in the shells and open pores in the gaps; and a volume of p-phase disposed in the open pores and the closed pores. In some embodiments, an all-solid-state battery comprises a solid electrolyte disposed on the composite anode architecture.

[0012] In some embodiments, an all-solid-state battery further comprises an interconnection between the plurality of shells. In some embodiments, an all-solid- state battery further comprises an interconnection between the plurality of shells and the plurality of shells are extrinsically interconnected using one dimensional (1 D) components, two dimensional (2D) components, or three dimensional (3D) components. In some embodiments, an all-solid-state battery further comprises an interconnection between the plurality of shells and the plurality of shells are intrinsically interconnected through sintering.

[0013] In some embodiments, an areal porosity varies throughout the composite anode architecture compared to a volumetric porosity of the composite anode architecture. In some embodiments, an areal porosity varies throughout the composite anode architecture compared to a volumetric porosity of the composite anode architecture and an areal porosity of the composite anode architecture at an interface of the composite anode architecture and the solid electrolyte is lower compared to a volumetric porosity of the composite anode architecture.

[0014] In some embodiments, the volume of p-phase is formed of at least one of lithium (Li), sodium (Na), or potassium (K). In some embodiments, the closed pores have a shortest cross-sectional width of less than 800 nm. In some embodiments, the mixed ion-electron conducting shells have a thickness of 2- 30% of their cross-sectional width. In some embodiments, a true contact area between the composite anode architecture and the solid electrolyte is greater than 50% of a nominal contact area with the solid electrolyte. In some embodiments, the all-solid-state battery further comprises a composite cathode disposed on the solid electrolyte; and a current collector disposed on the composite cathode.DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0015] The manner and process of making and using the disclosed embodiments may be appreciated by reference to the figures of the accompanying drawings. It should be appreciated that the components and structures illustrated in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the concepts described herein. Like reference numerals designate corresponding parts throughout the different views. Furthermore, embodiments are illustrated by way of example and not limitation in the figures, in which:

[0016] FIG. 1 is a cross-sectional side view of an all-solid-state battery (ASSB) including a composite anode architecture;

[0017] FIG. 2 is a cross-sectional top view of a composite anode architecture, such as the composite anode architecture of FIG. 1 , at the interface of the solid electrolyte and the composite anode architecture;

[0018] FIG. 3 is a cross-sectional top view of a composite anode architecture, such as the composite anode architecture of FIG. 1 , at the interface of the solid electrolyte and the composite anode architecture including a quantity of P-phase stored in both the closed and open pores;

[0019] FIG. 4 is a cross-sectional top view of a conventional anode architecture, at the interface of a solid electrolyte (SE) and the anode architecture;

[0020] FIG. 5 is an image of a composite anode architecture, such as the composite anode architecture of FIG. 1 ;

[0021] FIG. 6 is a cross-sectional side view of an ASSB with a composite anode architecture after alkali metal stripping and an ASSB with a composite anode architecture after alkali metal plating; and

[0022] FIG. 7 is an ab initio computed equilibrium phase diagram at 0 K.DETAILED DESCRIPTION

[0023] FIG. 1 shows a cross-sectional side view of an all-solid-state battery (ASSB) including 100 including a composite anode architecture 120 (composite anode architecture may be referred to herein as a three dimensional (3D) mixed ionic-electronic conductor (MIEC) architecture). The composite anode architecture 120 for solid-state batteries includes a mixed ion-electron conductor having a plurality of shells spaced from one another by gaps, including closed pores in the shells and open pores in the gaps. A volume of p-phase is disposed in the open pores and the closed pores. The composite anode architecture 120 is disposed on a first current collector 110, with a solid electrolyte 130 is disposed on the composite anode architecture 120. A composite cathode 140 is disposed on the solid electrolyte (SE) 130, with a second current collector 150 disposed on the composite cathode 140.

[0024] The open and closed pores are formed from mixed ion-electron conducting shells, for example a mixed ion-electron conducting shell is given by reference numeral 126. The composite anode architecture 120 includes a plurality of closed pores, for example a closed pore is given by reference numeral 124, in the plurality of shells. The composite anode architecture 120 includes a plurality of open pores, for example an open pore is given by reference numeral 122, in the gaps between the plurality of shells. The mixed ion-electron conducting shells may be formed from porous carbon materials. The composite anode architecture 120 further comprises an interconnection between the mixed ion-electron conducting shells, for example two interconnections are given by reference numeral 128.

[0025] The open pores 122, closed pores 124, and shells of the pores 126 can have different shapes. The composite anode architecture with a plurality of pores is often constructed from particles with a hollow core, with said particles either spherical or rod-shaped. Between spherical particles, there are either open or closed pores, the shape of which is determined by the surrounding particles. Thecomposite anode architecture 120 may include open pores 122, closed pores 124, and shells of the pores 126 each with different shapes. The composite anode architecture 120 may include open pores 122, closed pores 124, and shells of the pores 126 with a plurality of different shapes. Multiple types of different shapes could be present in the same composite anode architecture.

[0026] The closed pores 124 in the plurality of closed pores may have an average shortest cross-sectional width of less than 800 nm. For interfacial diffusion to be the dominant mechanism, the smaller width is ideally the best. Experientially, it has been confirmed that widths up to 800 nm work notably well. The aspect ratio of the plurality of closed pores may be less than 10.

[0027] The shell of the pores 126 is manufactured accordingly, first, 9 ml of ammonia solution (32%) is added to an ethanol and water (160 ml) (7:1 , v / v) solution and stirred for 5 min. Second, 7 ml of tetraethyl orthosilicate is added and stirred for 15 min. Third, 0.8 g of resorcinol and 1.12 ml of formaldehyde is added to the solution and stirred overnight heated at 60 °C. Fourth, centrifuge the obtained solution and dry the sedimented powder. Fifth, place the dried powder in an alumina boat and heat-treat it at 700 °C for 5 hours in an argon (Ar) atmosphere. The product of this step is carbon-coated silicon dioxide powder. Sixth, add the heat-treated powder into 2 M NaOH aqueous solution at 60 °C for overnight to etch silicon dioxide core, leaving behind only the carbon shell. Seventh, centrifuge the obtained solution and dry the sedimented powder.

[0028] An electrode comprising stacked powders with hollow cores, such as the composite anode architecture 300, can be prepared by either a wet method or a dry method. For a wet method: first, mix the powders with dispersant containing polymeric binders (e.g., polyvinylidene fluoride in N-methylpyrrolidone or carboxylmethyl cellulose in deionized water); and second, coat the slurry onto a current collector using a doctor blade. For a dry method, mix the powder with polytetrafluoroethylene with weight ratio of 95:5.

[0029] The mixed ion-electron conducting shells 126 may have a thickness of about 2 (+ / - 1 %) to about 30% (+ / - 5%) of their cross-sectional width. The pore shells have a thickness of about 2% (+ / - 1 %) to about 30% (+ / - 5%) of their shortest cross-sectional width. Based upon calculations, the ratio between the minimum thickness of pore shells (w) and the width of pores (W) may be fromabout 10% (+ / - 5%) to about 50% (+ / - 5%), depending on the MIEC used, when there is no interfacial diffusion. When considering interfacial diffusion, a smaller ratio becomes possible. Experimentally it has been confirmed that a ratio as small as about 2% (+ / - 0.5%) works well.

[0030] For interfacial-diffusional Coble creep to be the dominant mechanism for lithium flow, interfacial area should be large. Interfacial area refers to the area that interfaces with a different phase (e.g., vacuum, air, or lithium) and over which lithium adatoms can diffuse, either as neutral species or positively charged species. Interfacial diffusivity is typically greater than lattice diffusivity, but the total volume of such an interface through which interfacial diffusivity applies is smaller than the total volume of bulk lattices through which lattice diffusivity applies. The interfacial area is considered large when its contribution to Li conductivity exceeds that of bulk lattice diffusion. For a given porosity, the interfacial area is larger when the pore shell-to-pore width ratio (w / W) is smaller. For carbonaceous materials, interfacial diffusion remains dominant when the ratio (w / W) is below 30%.Therefore, a thickness of 2-30% of the shortest cross-sectional width is notably useful. Other possible creep mechanisms are bulk diffusional Nabarro-Herring creep, where atoms diffuse through the bulk lattice of crystals, and hybrid diffusive-displacive dislocation creep, where dislocation motion is involved and assisted by the diffusion of vacancies.

[0031] In an embodiment, the composite anode architecture is designed for solid-state batteries and includes a mixed ionic-electronic conductor (MIEC); a plurality of open pores formed within the MIEC, to facilitate the transport of an alkali metal to store the alkali metal in the plurality of pores or release the alkali metal from the plurality of pores and a plurality of closed pores formed within the MIEC, to reduce direct contact of an alkali metal with a solid electrolyte (SE).

[0032] FIG. 2 shows a cross-sectional top view of a composite anode architecture 200, which may be similar to or the same as the composite anode architecture of FIG. 1 , at the interface of the SE and the composite anode architecture, for example the interface of the solid electrolyte 130 and the composite anode architecture 120 in FIG. 1 . The composite anode architecture 200 includes a plurality of mixed ion-electron conducting shells of pores (which may be similar to or the same as the mixed ion-electron conducting shells 126 inFIG. 1), for example a mixed ion-electron conducting shell of a pore is given by reference numeral 210.

[0033] FIG. 3 shows a cross-sectional top view of a composite anode architecture 300, which may be similar to or the same as the composite anode architecture 120 of FIG. 1 , at the interface of the SE and the composite anode architecture, for example the interface of the solid electrolyte 130 and the composite anode architecture 120 in FIG. 1 . The composite anode architecture 300 includes a porous structure with both open and closed pores formed from a plurality of mixed ion-electron conducting shells of pores (which may be similar to or the same as the mixed ion-electron conducting shells 126 in FIG. 1), for example a mixed ion-electron conducting shell of a pore is given by reference numeral 310.

[0034] A quantity of P-phase stored in both the closed and open pores, for example a portion of P-phase is given by reference numeral 320. With a fraction of the p-phase being stored in the open pores, the architecture will not completely prevent direct contact between the P-phase and the SE, as illustrated by reference numeral 330. The closed and opened pores provide an empty space, not taken up by the shells of the pores, for storing and releasing the P-phase, which may be referred to as reserved porosity. The reserved porosity may be greater than or equal to 40%. The reserved porosity may be greater than or equal to 30%. The reserved porosity may be greater than or equal to 25%.

[0035] The P-phase is released upon discharging and may be an alkali metal formed of at least one of lithium (Li), sodium (Na), or potassium (K). The composite anode architecture 300 does not release excess alkali metals during regular service of the battery when used by a consumer (after the factory formation process). The voltage cut-off can be adjusted to ensure that the Ml EC does not release energy during regular service operations.

[0036] The volume of the p-phase may be greater than or equal to about 40% (+ / - 5%). The volume of the P-phase may be greater than or equal to about 30% (+ / - 5%). The volume of the P-phase may be greater than or equal to about 25% (+ / - 5%). The lower limit of the porosity, for the 3D composite anode architecture to function effectively, is a porosity of about 25% (+ / - 5%). Below a porosity of 25%, the interfacial area for diffusion is reduced, causing diffusion through thebulk lattice over a certain distance to be required in some regions. The volume of P-phase is at least about 40% (+ / - 5%) of a total volume of the composite anode architecture. The volume of alkali metal may be greater than or equal to about 40% (+ / - 5%)of the total volume of the composite anode architecture. The volume of P-phase is at least about 30% (+ / - 5%) of a total volume of the composite anode architecture. The volume of alkali metal may be greater than or equal to about 30% (+ / - 5%) of the total volume of the composite anode architecture. The volume of P-phase is at least about 25% (+ / - 5%) of a total volume of the composite anode architecture. The volume of alkali metal may be greater than or equal to about 25% (+ / - 5%) of the total volume of the composite anode architecture.

[0037] The pore shells create a thin layer with significantly lower areal porosity in comparison to the volumetric porosity of the entire composite anode architecture at the interface between the SE and composite anode architecture. Volumetric porosity refers to the volume of pores divided by the nominal volume that the composite anode architecture occupies. For instance, take a composite anode architecture formed in a disk shape with a diameter of 10 mm, a thickness of 20 pm, and a width of 1 mg. The composite anode architecture is formed of carbon with a density of 2 g / cm3. Accordingly, the volumetric porosity is estimated to be 78%.

[0038] Areal porosity refers to the fraction of the interface between the solid electrolyte and the composite anode architecture where the two respective surfaces are not in direct contact. For instance, in FIG. 3, the areal porosity is defined as the p-phase, for instance the p-phase given by reference numeral 320, divided by the sum of the P-phase and the shells of the pores, for instance the mixed ion-electron conducting shell of a pore given by reference numeral 410 and the P-phase given by reference numeral 420. The areal porosity varies throughout the composite anode architecture compared to a volumetric porosity of the composite anode architecture.

[0039] A thin layer at the interface with the SE is constructed of MIECs comprising pores that exhibit significantly lower areal porosity compared to the volumetric porosity of the entire structure. A thin layer may refer to the pores and shells located at the interface of the composite anode architecture and SE (forexample the interface of the solid electrolyte 130 and the composite anode architecture 120 in FIG. 1 ). For example, an areal porosity of the composite anode architecture at an interface of the composite anode architecture and the solid electrolyte is lower compared to a volumetric porosity of the composite anode architecture.

[0040] For a 3D composite anode architecture to be competitive against conventional graphite anodes, in terms of volumetric capacity, the porosity and thus the volume fraction of the p-phase deposited in the pores as compared to the whole volume that the 3D composite anode architecture is occupying should be greater than 30%. However, depending on the materials comprising the 3D composite anode architecture, a porosity greater than 30% may or may not offer a gravimetric capacity competitive against a conventional graphite anode.

[0041] FIG. 4 shows a cross-sectional top view of a conventional MIEC architecture 400 (conventional MIEC architecture may be referred to an anode architecture) at the interface of a SE and an MIEC architecture. The conventional MIEC architecture 400 includes a honeycomb-type structure with only open pores. The conventional MIEC architecture 400 includes a plurality of mixed ion-electron conducting shells of pores, for example a mixed ion-electron conducting shell of a pore is given by reference numeral 410. The conventional MIEC architecture 400 includes p-phase stored in the open pores, for example a portion of p-phase is given by reference numeral 420.

[0042] A large portion of the P-phase is stored in the open pores, resulting in contact between the p-phase and the SE, as illustrated by reference numeral 430. However, comparing the contact between the SE and the p-phase from the composite anode architecture 400 to the conventional MIEC architecture 400, direct contact is significantly reduced in the composite anode architecture 400 compared to the conventional MIEC architecture 400 with only open pores.

[0043] The pore structure at the interface of the MIEC architecture at the SE and composite anode architecture interface adjusts the contact between the p- phase and the SE. The interface between the solid electrolyte and the composite anode architecture with both closed pores and open pores, such as the composite anode architecture 400, has a large contact area. At the interface, a small fraction of the p-phase fills in pores that will be in direct contact with the SE. In aconventional honeycomb-type structure with only open pores, such as the conventional MIEC architecture 400, the contact area between the solid electrolyte and the wall of the composite anode architecture is limited, and a large fraction of the P-phase filling in pores will be in direct contact with the SE. The true contact area between the composite anode architecture and the solid electrolyte is greater than 50% of a nominal contact area with the solid electrolyte.

[0044] FIG. 5 shows an image of a composite anode architecture 500, which may be similar to or the same as the composite anode architecture 120 of FIG. 1 , including a plurality of pore shells, for example a pore shell is given by reference number 510, and a plurality of interconnections, for example an interconnection is given by reference number 520. The pore shells in FIG. 5 are hollow carbon spheres, with carbon nanotubes forming interconnections between individual hollow carbon spheres. Materials used for interconnection purposes should not decompose when in contact with the volume of P-phase.

[0045] The pore shells may be intrinsically interconnected through sintering. The pore shells may be interconnected extrinsically using one dimensional (1 D) components, two dimensional (2D) components, or three dimensional (3D) components. 1 D or 2D components may for example include components like carbon nanotubes or polymeric binders. 3D components may include components integrated through the infiltration or infusion of a three dimensional (3D) medium into the open pores between the closed pores. The 3D medium may be a ceramic or metals stable against the P-phase.

[0046] Other possible interconnections include: U7N2I, LisN, LisOCI, U2OHCI, Na, K, Cs, Rb, Cu, Fe, Or, Ni, Ti, V, La, Nd, Ce, graphene, carbon nanotubes, carbon microfibers, carboxymethyl cellulose, polyvinylidene fluoride, and polyacrylic acid binder with or without 5 wt% polyrotaxanes. Multiple interconnects may be used. For example, carbon nanotubes and polymeric binders can be used simultaneously.

[0047] FIG. 6 is a cross-sectional side view of an ASSB including a composite anode architecture after alkali metal stripping 600 and an ASSB including a composite anode architecture after alkali metal plating 650.

[0048] The ASSB after alkali metal stripping 600 includes a first composite anode architecture 610 disposed on a first current collector 602, with a solidelectrolyte 604 is disposed on the composite anode architecture 610. A composite cathode 606 is disposed on the solid electrolyte 604, with a second current collector 608 disposed on the composite cathode 606.

[0049] As an example of metal stripping, assume the alkali metal of interest is Li metal. During metal stripping of the 3D mixed ionic-electronic conductor architecture (i.e., battery discharging), Li metal atoms will be oxidized to a Li-ion, losing an electron, resulting in the equation: Li (for an atom in the P-phase) -> Li+(for the MIEC or SE) + e’ (for the MIEC).

[0050] Li-ions resulting from the aforementioned oxidation reaction will be driven toward the solid electrolyte through MIEC by a gradient in electrochemical potential. Thus, the amount of p-phase in the composite anode architecture will decrease over time. Once fully stripped (i.e., a state-of-charge (referred to herein as SOC) of 0%), there will be no P-phase left in the 3D composite anode architecture, and the thickness of the 3D composite anode architecture will be at its smallest.

[0051] The ASSB after alkali metal plating 650 includes a second MIEC architecture 660 disposed on a first current collector 652, with a solid electrolyte 654 is disposed on the anode architecture 660. A composite cathode 656 is disposed on the solid electrolyte 654, with a second current collector 658 disposed on the composite cathode 656. Plating of alkali metal can induce local mechanical stress and result in thickness changes of the composite anode architectures. As an example, a 20 pm-thick composite anode architecture with a porosity of 75% can store 3 mAh / cm2of fully dense lithium metal. However, in practice, the lithium may not remain fully dense, resulting in expansion of the composite anode architecture. The thickness can thus change monotonically as a function of state of charge. The variation should be kept as small as possible.

[0052] During metal plating of the 3D mixed ionic-electronic conductor architecture (i.e., battery charging), Li+ions will be reduced to Li metal, acquiring an electron and resulting in the equation: Li+(for the MIEC or SE) + e- (for the MIEC) -> Li (for an atom in the P-phase). This net increase in the number of atoms in a local volume leads to an increase in pressure in the surrounding solid component. The pressure in the p-phase can be relaxed by plastic deformation, driven by a pressure gradient and shear stress. During this process, the p-phaseis driven towards the pores in the 3D composite anode architecture. If the transport of Li atoms is not sufficiently fast, a fraction of the produced Li atoms will remain accumulated at the interface between hollow particles, causing an increase in the thickness of 3D composite anode architecture. If the 0-phase deposited between hollow particles becomes stripped in the subsequent charging process, the thickness of the composite anode architecture could be reduced back to before plating.

[0053] The thickness of the composite anode architecture can vary. As illustrated in FIG. 6, the composite anode architecture 610 of the ASSB after alkali metal stripping 600 has a different thickness compared to the composite anode architecture 660 of the ASSB after alkali metal plating 650. The composite anode architecture 660 is thicker compared to the composite anode architecture 610. The composite anode architectures’ thickness variation remains less than 10%, regardless of the state of charge.

[0054] The shells in composite anode architecture 660 are asymmetric. Development and relaxation of pressure could differ from point to point in the 3D composite anode architecture, causing the arrangement of hollow particles (or shells) to be less symmetric than in the initial composite anode architecture. Accordingly, there could be a rearrangement of the hollow particles and hence a thickness variation, even if there is sufficient porosity to accommodate the 0- phase in principle. However, the variation will be smaller than in the 3D composite anode architecture without hollow particles (or shells). The initial composite anode architecture may not be as symmetric (meaning it may be asymmetric or less symmetric) as illustrated by composite anode architecture 610.

[0055] FIG. 7 shows an ab initio computed equilibrium phase diagram at 0 K (which may be referred to herein as an equilibrium phase diagram) 700. The composite anode architecture (for example the composite anode architecture 120 in FIG. 1) is an end-member phase directly connected to the alkali metal by a tieline in an equilibrium phase diagram. For example, titanium carbide (TiC) is a MIEC having a direct tie-line with lithium, as disclosed in FIG. 7.

[0056] Equilibrium phase diagram 700 is a ternary phase diagram constructed based on density functional theory calculations at 0 K. The equilibrium phase diagram, and thus the end-member phases, could differ at ambient temperature.Moreover, metastable phases can be kinetically stabilized against alkali metals and function as if they are end-member phases directly connected to the alkali metal. Examples of said material include Lis. sSi. In addition, the composite anode architecture can initially be constructed of non-end-member phases, which will be lithiated during charging and remain lithiated throughout cycling, thereby functioning as if they are end-member phases. Examples of said materials include carbonaceous materials.

[0057] The functionalities of this architecture can be categorized into four key aspects. Firstly, it provides a designated empty space for storing and releasing the P-phase (reserved porosity). Secondly, it serves to encapsulate the p-phase, reducing direct contact with the solid electrolytes and thereby minimizing the loss of lithium due to undesired side reactions. Thirdly, it creates a substantial true contact area with the solid electrolyte, thus preventing localized current concentration. Lastly, it offers ample inner surfaces for charge transfer reactions and facilitates lithium diffusion.

[0058] Consequently, 3D IECs with such an architecture can achieve the following four significant benefits: dimensional stability, enhanced coulombic efficiency; prevention of short-circuiting; and improved rate capability. In reference to dimensional stability, by limiting the overall stack strain to as close to zero as possible, independent of the state of charge, the disclosed architecture ensures dimensional stability. In reference to enhanced coulombic efficiency, the encapsulation of the P-phase reduces side reactions, resulting in improved Coulombic efficiency and extended cycle life. In reference to the prevention of short-circuiting, the extensive true contact area prevents short-circuiting due to high current densities in localized regions, promoting long-term stability. True contact area refers to the area on which charge transfer reactions can take place. The disclosed architecture enables control over the contact area, for instance, by varying the diameter of hollow carbon spheres. Generally, a larger true contact area is preferable. The disclosed composite anode architecture may have a true contact area greater than twice the nominal contact area with the SE.

[0059] The additional contact area provided by the 3D composite anode architecture can reduce charge transfer resistance. However, for charge transfer reactions to take place within the 3D composite anode architecture, Li-ions needto travel a longer distance (i.e., extending beyond the SE). This longer transport distance can result in a higher overpotential. Thus, the additional contact area should be large enough to compensate for the longer transport distance. Assuming that the thickness and effective Li conductivity of the 3D composite anode architecture are similar to the thickness and Li-ion conductivity of the SE, the true contact area should be greater than twice the nominal contact area with the SE. If not, a larger true contact area would not confer an advantage in terms of overpotential (i.e., dissipated energy).

[0060] In reference to improved rate capability, the design facilitates kinetics, leading to enhanced rate capability. In summary, this composite anode architecture offers a promising solution for addressing several critical challenges in ASSB electrodes, making them safer, more efficient, and longer-lasting.

[0061] The disclosed architecture provides a number of advantages over conventional technologies. Various conventional composite anode architectures have been proposed to mitigate the challenges posed by the mechanically stressful and chemically corrosive P-phase and thereby ensure the reliability of ASSBs. These proposed MIEC architectures can be broadly categorized into two main groups based on their functionalities: (1 ) dense interlayer MIECs and (2) open-porous host MIECs.

[0062] Conventional interlayer MIECs are characterized by having low porosity (less than 40%), lack of closed pores, and inner pores with dimensions less than 100 nanometers. While conventional MIECs may offer these three advantages, they exhibit a notable limitation: the p-phase forms a separate layer from the MIECs due to their limited porosity, and as a result, they do not provide the first functionality, which is dimensional stability. On the other hand, the conventional host MIECs proposed to date offer the first and last functionalities, but they are unable to provide sufficient protection for solid electrolytes against the mechanical and chemical challenges posed by the p-phase. This is primarily because these host MIECs are predominantly open-porous.

[0063] In contrast, the disclosed composite anode architecture combines the functionalities of both interlayer MIECs and host MIECs by incorporating closed pores. These pore shells effectively act as an interlayer MIEC, while the inner volume accommodates the p-phase. This design minimizes the weight andvolume of additional materials required to achieve all the functionalities mentioned earlier, making it a promising solution for building reliable ASSBs.

[0064] Various embodiments of the concepts, systems, devices, structures and techniques sought to be protected are described herein with reference to the related drawings. Alternative embodiments can be devised without departing from the scope of the concepts, systems, devices, structures and techniques described herein. It is noted that various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and / or positional relationships, unless specified otherwise, can be direct or indirect, and the described concepts, systems, devices, structures and techniques are not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship.

[0065] As an example of an indirect positional relationship, references in the present description to forming layer "A" over layer "B" include situations in which one or more intermediate layers (e.g., layer "C") is between layer "A" and layer "B" as long as the relevant characteristics and functionalities of layer "A" and layer "B" are not substantially changed by the intermediate layer(s).The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms "comprises," "comprising, "includes," "including," "has," "having," "contains" or "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

[0066] The terms "one or more" and "one or more" are understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms "a plurality" are understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term "connection" can include an indirect "connection" and a direct "connection".

[0067] References in the specification to "one embodiment,” "an embodiment," "an example embodiment," etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment can include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0068] For purposes of the description hereinafter, the terms "upper," "lower," "right," "left," "vertical," "horizontal, "top," "bottom," and derivatives thereof shall relate to the described structures and methods, as oriented in the drawing figures. The terms "overlying," "atop," "on top, "positioned on" or "positioned atop" mean that a first element, such as a first structure, is present on a second element, such as a second structure, where intervening elements such as an interface structure can be present between the first element and the second element. The term "direct contact" means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary conducting, insulating or semiconductor layers at the interface of the two elements.

[0069] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0070] The terms “approximately” and “about” may be used to mean within ±20% of a target value in some embodiments, within ±10% of a target value in some embodiments, within ±5% of a target value in some embodiments, and yet within ±2% of a target value in some embodiments. The terms “approximately” and “about” may include the target value.

[0071] It is to be understood that the disclosed subject matter is not limited in its application to the details of construction and to the arrangements of thecomponents set forth in the following description or illustrated in the drawings. The disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the disclosed subject matter. Therefore, the claims should be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the disclosed subject matter.

[0072] Although the disclosed subject matter has been described and illustrated in the foregoing exemplary embodiments, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the details of implementation of the disclosed subject matter may be made without departing from the spirit and scope of the disclosed subject matter.

Claims

What is claimed is:1 . A composite anode architecture for solid-state batteries, comprising: a mixed ion-electron conductor having a plurality of shells spaced from one another by gaps and having closed pores in the shells and open pores in the gaps; and a volume of P-phase disposed in the open pores and the closed pores.

2. The composite anode architecture for solid-state batteries of claim 1 , further comprising an interconnection between the plurality of shells.

3. The composite anode architecture for solid-state batteries of claim 2, wherein the plurality of shells are extrinsically interconnected using one dimensional (1 D) components, two dimensional (2D) components, or three dimensional (3D) components.

4. The composite anode architecture for solid-state batteries of claim 2, wherein the plurality of shells are intrinsically interconnected through sintering.

5. The composite anode architecture for solid-state batteries of claim 1 , wherein an areal porosity varies throughout the composite anode architecture compared to a volumetric porosity of the composite anode architecture.

6. The composite anode architecture for solid-state batteries of claim 1 , wherein the volume of P-phase is formed of at least one of lithium (Li), sodium (Na), or potassium (K).

7. The composite anode architecture for solid-state batteries of claim 1 , wherein the closed pores have a shortest cross-sectional width of less than 800 nm.

8. The composite anode architecture for solid-state batteries of claim 7, wherein the plurality of shells have a thickness of 2-30% of their cross-sectional width.

9. The composite anode architecture for solid-state batteries of claim 1 , wherein the volume of p-phase is at least 40% of a total volume of the composite anode architecture.

10. An all-solid-state battery, comprising: a current collector; a composite anode architecture disposed on the current collector, the composite anode architecture comprising: a mixed ion-electron conductor having a plurality of shells spaced from one another by gaps and having closed pores in the shells and open pores in the gaps; and a volume of p-phase disposed in the open pores and the closed pores; and a solid electrolyte disposed on the composite anode architecture.1 1 . The all-solid-state battery of claim 10, further comprising an interconnection between the plurality of shells.

12. The all-solid-state battery of claim 11 , wherein the plurality of shells are extrinsically interconnected using one dimensional (1 D) components, two dimensional (2D) components, or three dimensional (3D) components.

13. The all-solid-state battery of claim 11 , wherein the plurality of shells are intrinsically interconnected through sintering.

14. The all-solid-state battery of claim 10, wherein an areal porosity varies throughout the composite anode architecture compared to a volumetric porosity of the composite anode architecture.

15. The all-solid-state battery of claim 14, wherein an areal porosity of the composite anode architecture at an interface of the composite anode architecture and the solid electrolyte is lower compared to a volumetric porosity of the composite anode architecture.

16. The all-solid-state battery of claim 10, wherein the volume of p-phase is formed of at least one of lithium (Li), sodium (Na), or potassium (K).

17. The all-solid-state battery of claim 10, wherein the closed pores have a shortest cross-sectional width of less than 800 nm.

18. The all-solid-state battery of claim 10, wherein the mixed ion-electron conducting shells have a thickness of 2-30% of their cross-sectional width.

19. The all-solid-state battery of claim 10, wherein a true contact area between the composite anode architecture and the solid electrolyte is greater than 50% of a nominal contact area with the solid electrolyte.

20. The all-solid-state battery of claim 10, further comprising a composite cathode disposed on the solid electrolyte; and a current collector disposed on the composite cathode.

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