Solid-state rechargeable lithium battery with solid-state electrolyte

Abstract

A lithium battery includes a solid cathode and a solid electrolyte (SSE), wherein a structurally continuous block of material comprises the solid cathode and the SSE. The structurally continuous solid block of material has a first chemical composition in the solid cathode and a second chemical composition, different from the first chemical composition, in the SSE. The SSE overlies the solid cathode, without any physical separation or interface therebetween. A method for fabricating a lithium battery includes placing a first layer of particles of an electrolyte material of a first composition on top of a second layer of particles of a cathode material of a second composition, forming a stack; and compressing and heating the stack of first and second layers to form a continuous solid material. The formed material has a solid electrolyte (SSE) characterized by the first composition and a solid cathode characterized by the second composition.

Claims

1. A lithium battery comprising: an anode; a solid cathode having a first chemical composition, wherein the first chemical composition is a first phosphate, optionally doped with a first dopant; and a solid electrolyte (SSE) having a second chemical composition, wherein the second chemical composition is a second phosphate, optionally doped with a second dopant, the second chemical composition being different from the first chemical composition; wherein the SSE overlies, and is in continuous and integral contact with, the solid cathode such that the SSE and the solid cathode form a continuous solid material with no physical separation between the solid cathode and the SSE; and wherein the anode overlies and is in direct contact with the solid SSE.

2. The lithium battery as in claim 1, wherein a major constituent of the first chemical composition comprises one or more compositions of LiM′PO.sub.4, where M′ comprises one or more of the following elements: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn; and wherein a major constituent of the second chemical composition comprises one or more compositions of LiM″PO.sub.4, where M″ comprises one or more of the following elements: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn.

3. The lithium battery as in claim 2, wherein the major constituent of the first chemical composition is LiFePO.sub.4; and wherein the major constituent of the second composition is LiFe.sub.xMn.sub.(1-x)PO.sub.4, where 0≤x<1.

4. The lithium battery as in claim 1, wherein the solid cathode comprises a first layer of first particles of the first chemical composition, with an average particle dimension of 1 μm or less; wherein the SSE comprises a second layer of second particles of the second chemical composition, with an average particle dimension of 1 um or less; and wherein the first and second layers of particles are compressed and fused together to form the continuous solid material.

5. The lithium battery as in claim 4, wherein the particles of the first chemical composition are coated with a material that conducts ions and electrons, and the particles of the second chemical composition are either completely uncoated or are coated with a material that conducts ions but does not conduct electrons.

6. The lithium battery as in claim 1, further comprising an electrically insulating material separating a plurality of islands, each island comprising a block of material comprising an anode region of that island overlying an SSE region of that island, the SSE region of that island overlying a cathode region of that island overlying; wherein the electrically insulating material is characterized by a compliance sufficient to reduce a risk of crack formation in any of the blocks; and wherein the anode region of each island has a top surface co-planar with anode regions of top surfaces of each other island in the lithium battery.

7. The lithium battery as in claim 6, wherein the electrically insulating material separating the blocks is a fluorinated polymer.

8. The lithium battery as in claim 1 wherein the SSE and the solid cathode in combination either form a single crystal characterized by a b-axis that is oriented perpendicular to a top surface of the SSE, or a plurality of crystallites characterized by a b-axis that is oriented perpendicular to a top surface of the SSE.

9. The lithium battery as in claim 1 wherein the first chemical composition includes a cathode dopant comprising one element, or a combination of elements that increase the conductivity for lithium ions and/or electrons, and/or decrease the volume change, when lithium moves into or out of the material.

10. The lithium battery as in claim 9, wherein the element or elements in the cathode dopant are chosen from among elements characterized by oxidation states of x.sup.+ or x.sup.− where x is any positive integer other than 2, and which contribute either holes or electrons that increase the conductivity for electrons.

11. The lithium battery as in claim 1, wherein the second chemical composition includes an SSE dopant comprising one element, or a combination of elements, that will either increase the conductivity for lithium ions, or decrease the conductivity for electrons, or increase the conductivity for lithium ions and decrease the conductivity for electrons.

12. The lithium battery as in claim 1, wherein the anode is a metallic lithium anode.

13. The lithium battery as in claim 12, additionally comprising a metal contact to the metallic lithium anode, the metal contact comprising aluminum, another metal, or a metal alloy, that is strongly wetted by lithium.

14. The lithium battery as in claim 13, wherein a surface of the SSE in contact with the metallic lithium anode is free of any carbonates, hydroxides or other contaminants, and includes a coating of LiF, of thickness no greater than a thickness corresponding to 2 atomic layers thereof, such that metallic lithium will wet the surface of the electrolyte uniformly and avoid creating current concentrations and hot spots.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is an illustration of a typical prior-art commercial lithium battery, shown in cross-section.

(2) FIG. 2 is an illustration of a lithium battery according to some embodiments of the current invention, shown in cross-section.

(3) FIG. 3 is an illustration of a lithium battery according to some embodiments of the current invention, shown in a top-down view, where the vertically continuous solid-state battery material is broken into islands with a soft material between the islands to allow for volume expansion.

(4) FIG. 4 is an illustration of a lithium battery according to embodiments of the current invention, shown in cross-section. showing the construction of a solid-state battery, with the cathode, solid-state electrolyte (SSE), and the lithium metal anode, and with a protective coating on the SSE.

DETAILED DESCRIPTION

(5) In one embodiment, illustrated schematically in FIG. 2 (in cross-section), a solid-state lithium battery (200) is formed using a continuous block of solid material (201) which functions as both the cathode (201a) and the solid-state electrolyte (201b). The continuous block of solid material 201 is attached to a conductive substrate, such as aluminum (202). The lower portion (201a) of the continuous block 201 closest to the aluminum substrate (202), has a chemical composition (a primary molecular constituent, plus, in some cases, one or more dopants) chosen to increase its electron and ion conductivity and/or minimize the volume change when lithium exits the material during charging. This section 201a forms the cathode of the battery, with good conductivity for both ions (204b) and electrons (204a).

(6) The upper portion of the continuous solid material is a section (201b) that forms the solid-state electrolyte (SSE). In one embodiment, its primary chemical constituents and any dopants are chosen to increase its conductivity for ions and reduce its conductivity for electrons to a very low level (close to completely insulating). In contact with the top surface of the SSE layer 201b is a layer of metallic lithium that forms the anode (203). Contacting the top surface of anode 203 is a high conductivity layer 202b, typically of aluminum like substrate 202. Contacts 202a and 202c to the aluminum substrate (202) and to the top layer of aluminum (202b) respectively allow electrons to flow from the battery into the external electrical circuit (205).

(7) In some embodiments, the solid material is made from one or more compositions of LiMPO4, where M stands for one element, or a combination of elements, from among: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn. In one embodiment, the cathode section of the LiMPO4-material is doped to increase its electron and ion conductivity, and the SSE section of the LiMPO4-material is not doped and retains its normally very low electron conductivity.

(8) In one of the LiMPO.sub.4 embodiments, M=Fe in the cathode and in the SSE. The cathode section is doped LiFePO4-material and the SSE section is undoped LiFePO.sub.4 material.

(9) In another embodiment, where M is Fe in the cathode section and a combination of Fe and Mn in the SSE section, the cathode section is doped LiFePO.sub.4 and the SSE section is undoped LiMn.sub.xFe.sub.(1-x)PO.sub.4, where 0≤x≤1. Undoped LiMPO.sub.4 has a 4 times lower electron conductivity than undoped LiFePO4, circa 10{circumflex over ( )}-9 S/cm at room temperature. However, its ion conductivity may be a little too low, depending on the application. It also has a slightly different lattice volume than LiFePO.sub.4, about 3% larger.

(10) In various embodiments, the dopant is one element, or a combination of elements, selected from a list that includes: Na, Ca, Mg, Zn, Cu, Ti, Cr, V, Mn, Co, Zr, Y, Al, Ga, Si, Ge, Sn, Nb, Mo, Sm, Eu, Yb, C, N, F, CI, S or any other elements that will not make the material chemically unstable. Many dopants incorporated into LiMPO.sub.4 have been found to result in an increase in the electron and ion conductivity.

(11) In one embodiment, doping elements for the cathode region are chosen that will partially substitute for the M atoms in LiMPO.sub.4, and whose ionic radius is the same or smaller than the ionic radius of M.sup.2+. For example, the ionic radius of Fe2+ is 78 pm, while the ionic radius of Mg2+ is 72 pm. A doping of 5% of Mg in LiFePO.sub.4 has been found to improve the ion conductivity by 4 times and improved the electron conductivity by 50,000 times. With 5% Mg doping, the conductivity for ions and electrons became approximately equal. It is important to improve the ion conductivity to support fast charging and discharging, but it is essential to dramatically improve the electron conductivity in the cathode region for the battery to function at all. The doping must change LiMPO.sub.4 from an electron insulator to an electron conductor. When charging or discharging at high rates, good conductivity is required for both ions and electrons.

(12) In one embodiment, doping elements are chosen that favor higher oxidation states than 2+, like Cr.sup.3+, V.sup.3+, Ti.sup.4+ or Zr.sup.4+. With their higher oxidation states, these elements create electrons or holes that enhance the electron conductivity of LiMPO.sub.4. In one embodiment, doping elements are chosen from among fluorine (F—) and other anions that can substitute for oxygen atoms, whose oxidation state is 2-(O.sup.2−) and improve the electron and/or ion conductivity. In one embodiment, Si atoms are substituted for P atoms. Finally, in one embodiment, doping elements are a combination of elements, with a smaller ionic radius, like Mg, and/or a higher oxidation state, like V3+, and/or a lower oxidation state than the ions they replace, like F— or Si.sup.4+.

(13) In one embodiment, the amount of doping in either the cathode or SSE section is limited to 10%. In many experiments, too much doping has been found to be counterproductive. Depending on the element chosen, best results are often obtained with a few percent of the element doped into LiMPO.sub.4. When combinations of elements are chosen, best results are often obtained when the total concentration of the multiple dopants is less than 10%.

(14) In LiFePO.sub.4, and most LiMPO.sub.4 materials, lithium ions travel through channels along the b-axis of the crystal. In one embodiment, dopants like Mg.sup.2+, with ionic radii smaller than Fe.sup.2+ ions, and F— with ionic radii smaller than O.sup.2−ions, act upon the LiFePO.sub.4 crystal structure to create lithium vacancies, lower the activation energy for lithium-ion movement, and thus increase the Li-ion conductivity. In addition, the choice of the element or elements, M, in LiMPO.sub.4 can change the conductivity for lithium ions and also the volume change, when lithium exits the material.

(15) Usually, dopants are considered to be elements that enter the lattice of a crystal and substitute for atoms in the crystal. In one embodiment, the dopants chosen do not enter the crystal, instead they accumulate at the grain boundaries of the crystallites and increase the conductivity of the entire crystallite by greatly increasing the electron and/or ion conductivity of the grain boundaries.

(16) In one embodiment, the cathode region is made with a composite material made with particles, of a doped or undoped material, that are coated with some form of conductive material, such as graphite, lithium, or a conductive metal oxide. The SSE region is also made with particles, but without the conductive coating. Layers of the two materials are compressed, heated, and fused together to form a continuous solid material without a physical separation between the cathode and the SSE. The materials, the doping, and the conductive coating are chosen so that the thermal expansion of the cathode region is similar to the thermal expansion of the SSE region.

(17) In some embodiments, the continuous material for the cathode and SSE is fabricated by the following method. Doped or undoped, coated or uncoated powders are produced for the cathode and for the SSE regions, with particle dimensions of 1 μm or less. The powder for the cathode region is placed down as a layer, then the powder for the SSE region is placed down in a layer on top of the first layer. If a transition layer is desired, it is placed on top of the first layer and then the SSE layer is placed on top of the transition layer. Finally, all layers of powder are compressed and heated together at the same time until they fuse to form a dense, continuous material. Material originally placed at the bottom stays at the bottom and material originally placed at the top stays at the top. Where the layers of powder meet, the final, dense, continuous material will transition smoothly from the material of one layer to the material of the next with no discernable separation or interface between the layers, and with complete and continuous contact between the layers.

(18) In some prior art LiFePO.sub.4 cathodes, the cathode material is a composite, comprised of 3 different materials: LiFePO.sub.4 particles, carbon or graphite particles, and a binding material, like poly vinylidene fluoride, that holds the composite material together. In various embodiments of this invention, the continuous material that contains both the cathode and the SSE is not a composite. The cathode and SSE sections are both homogeneous materials. A cross-section through either of them will reveal a material with a uniform composition. If made with particles, all particles in either the cathode or the SSE are of the same material composition and are sintered together, not held together by a binder.

(19) In one embodiment, to minimize possible cracking of the solid material from internal stress, the boundary between the cathode and the SSE sections is graded by transitioning slowly from 100% of the cathode powder to a mixture, and then, to 100% of the SSE powder. After the powder layers are placed down, then they are compressed, heated and fused together to form a continuous material. A graded interface will spread any internal mechanical stress over a larger thickness of the continuous, solid material.

(20) Doping and grading as part of a continuous LiMPO.sub.4 material is easily accomplished. In one embodiment, LiMPO.sub.4 material is formed from precursors that are ground and heated to form small particles of the final material. Doping is achieved by forming the small particles of LiMPO.sub.4 from a mixture of several chemicals that include the dopant as an oxide (eg. MgO), a phosphate (eg. MnPO.sub.4), an oxalate (eg. MgC2O.sub.4), a lithium compound (eg. LIE), etc. After the doped powders are created, they are then layered, compressed and heated together to create the final, dense LiMPO.sub.4 material.

(21) In LiMPO.sub.4 materials, lithium-ion conduction is along the b-axis of the crystal or crystallites. In one embodiment, the LiMPO.sub.4 material is either a single crystal or multi-crystalline with crystallites. The crystal or crystallites are oriented so that the b-axis is perpendicular to the surface and aligned with the direction of lithium-ion flow. In one embodiment, during fabrication, the powders are compressed and heated in the presence of a strong magnetic field to orient the b-axis. Ions and electrons are conducted one-dimensionally in LiMPO.sub.4 along the b-axis. Aligning the b-axis with the current flow will improve conductivity, especially for ions.

(22) Changes in volume of LiMPO.sub.4 during charging and discharging can cause cracks in the material that degrade its capacity with each cycle. For example, in LiFePO.sub.4, the a, b, and c axes expand and contract by +4%, +4%, and −2%, respectively, when lithium exits and the material becomes FePO.sub.4. In one embodiment, with the b-axis oriented perpendicular to the surface, the direction of the a and c axes in multiple crystallites are oriented randomly in the direction parallel to the surface. Thus, the expansion parallel to the surface is the average of the expansion of the a and c axes, when lithium exits.

(23) In the continuous material that contains both the SSE and the cathode, the SSE region remains fully lithiated, while the cathode region changes from LiMPO.sub.4 to MPO.sub.4 and back again, during charging and discharging. The electron conductivity of the SSE is so low that no redox reactions can occur in a reasonable time frame (M.sup.2+←.fwdarw.M.sup.3+), and the material remains LiMPO.sub.4.

(24) When the battery is fully charged, the cathode is MPO.sub.4 and the SSE is LiMPO.sub.4. At the transition region between the cathode and SSE, there are shear stresses caused by the differences in volume expansion. For LiFePO.sub.4, the Young's modulus is circa 124 GPa, the bulk modulus is circa 94 GPa, and the shear modulus is circa 48 GPa. The material is a ceramic, with a high shear modulus, and the effect of the volume change gets spread over a large thickness, compared with the total thickness of the continuous material.

(25) When the battery is fully charged, in a direction parallel to the top or bottom surface (as viewed in FIG. 2) of the battery, the SSE will experience a compressive stress trying to decrease its dimensions parallel to the top or bottom surface, and the cathode region, which is typically much larger than the SSE region, will experience a much smaller tensile stress in the same directions. As the battery discharges, and both materials become fully lithiated, these stresses will decrease toward zero. In the direction normal to the surface, the material just contracts and expands. At any level in the thickness of the material, there is no difference in the contraction or expansion. Thus, there is no stress perpendicular to the surface.

(26) In both the SSE and the cathode region, the continuous LiMPO.sub.4 material will expand and contract. Since this material is a ceramic, since the expansion or contraction throughout the continuous material is large (1-2%), and since the stresses are high, like all ceramics, LiMPO.sub.4 material can form cracks. During discharging, metallic lithium can accumulate in the cracks, rather than re-enter the MPO.sub.4 material and re-form LiMPO.sub.4. Lithium stuck in the cracks becomes unavailable for future charge-discharge cycles, thus reducing the capacity of the battery. It is the redox reaction of LiMPO.sub.4 on one side of the separator with lithium metal on the other side that creates the battery. Lithium metal on both sides does nothing. Lithium metal in the cracks is called “dead lithium”. It is no longer part of the battery capacity.

(27) There are a number of ways to minimize the formation of cracks. In one embodiment, the LiMPO.sub.4 material forming the cathode and the SSE, with a metallic lithium anode on top is divided into islands, in the direction parallel to the surface, with a compliant, insulating material between the islands. This is analogous to a concrete sidewalk, in which the concrete is divided into sections, that are separated by a compliant material that allows each section to expand or contract. Expansion or contraction of the LiMPO.sub.4 material parallel to the top surface is absorbed by the compliant material between islands. Expansion or contraction of the LiMPO.sub.4 and/or the metallic lithium anode perpendicular to the surface is allowed by the open space above the SSE.

(28) In one embodiment, illustrated as a top-down view in FIG. 3, a lithium battery (300) comprises many islands. In one embodiment, each island (301) comprises a block of material with both cathode and SSE regions, and a layer of metallic lithium anode material above the SSE layer. Separating these islands is an insulating, compliant material (302), that is easily stretched or compressed.

(29) In one embodiment, the insulating, compliant material 302 is fabricated pre-compressed so that when the LiMPO.sub.4 loses lithium, becomes MPO.sub.4, and contracts, the separating material between islands expands and fills any gaps. Thus, the island separating material maintains close contact with the sides of the cathode plus SSE and prevents any lithium metal from the anode from flowing around the side of the SSE material and contacting the side of the cathode material.

(30) In one embodiment, the island separating material 302 is poly vinylidene fluoride (PVDF) or another compressible fluorinated polymer. The compliant and chemically inert, PVDF allows the cathode, SSE and anode materials to expand or contract. With fluorine atoms at its surface, PVDF is nicely wet by lithium metal.

(31) Illustrated in FIG. 4 is the battery 400, similar to battery 200 as shown in FIG. 2 (in cross-section), but with the addition of the island separating material (407) surrounding the continuous material that contains both cathode and SSE regions, and the anode material. It prevents lithium metal from migrating down the sides and contacting the cathode or the aluminum below the cathode (402). Also shown are the bottom aluminum contact (402a) to the aluminum that contacts the cathode (402) and the top aluminum contact (402c) to the aluminum or other metal (402b) contacting the lithium anode (403). External circuit 405, electrons 404b and ions 404a are shown, corresponding to elements 205, 204b and 204a in FIG. 2.

(32) In one embodiment, the SSE material is on top of the cathode and also on the sides. This is illustrated in FIG. 4, where the SSE (401b) is shown both on top and on the sides of the cathode (401a). Surrounding the cathode material with SSE on the sides, except for the cathode contact to the bottom aluminum (402), provides added protection against electrons moving down the sides of an island in any gaps that may exist between the island of solid cathode/SSE material and the compliant material between the islands. As described previously, in another embodiment, the SSE layer is only on top of the cathode and the complaint material between islands is pre-compressed to eliminate any gaps through which electrons or lithium metal could flow around the SSE layer and directly contact the cathode layer.

(33) In one embodiment, the island separator material (407) extends above the SSE and forms a compartment to contain the lithium metal anode, that expands and contracts to fill or empty the compartment during charging and discharging. The aluminum substrate below the cathode region (402) and the aluminum (402b) that contacts the lithium anode (403) are continuous and connect all islands. Both the top and bottom aluminum layers contact and seal against the island separator material.

(34) In one embodiment, the sides of the separator material above the SSE layer are coated with lithium, magnesium, or aluminum metal. In one embodiment, the separator material above the SSE is replaced with a conductive material, such as aluminum, that forms a compartment for lithium metal. In another embodiment, the island separator material extends only to the top of the SSE layer. The lithium metallic anode (403) and the top aluminum contact (402b) are continuous over the top of the separator material and connect all islands.

(35) In one embodiment, the cathode and the SSE sections are both made from LiMPO.sub.4 materials that have coefficients of thermal expansion that are close to each other. Thus, differential volume changes between the cathode and SSE sections with temperature changes are minimized. In one embodiment, volume changes in LiMPO.sub.4 during charge-discharge cycles are minimized by choosing the element or combination of elements for M that minimize volume changes. In one embodiment, doping elements are chosen that also minimize volume changes during charge-discharge cycles.

(36) In one embodiment, prior to compressing and heating the powder particles to form the continuous material for the cathode and SSE, the particles are coated to lubricate the grain boundaries in the final material and allow it to expand and contract along the grain boundaries with less tendency to form cracks. In one embodiment, the powder particles for the cathode region are coated with a very thin layer (circa 1 nm) of extra lithium metal that will collect at and lubricate the grain boundaries. In one embodiment, the powder particles for the cathode region are coated with a very thin layer of graphite (circa 1 nm) that will collect at and lubricate the grain boundaries. In one embodiment, the powder particles for the SSE region are coated with a thin layer of an insulating coating that conducts lithium ions, but not electrons, like LiF (1-2 atomic layers).

(37) In one embodiment, the SSE section of the continuous material is undoped LiFePO.sub.4 or undoped LiMPO.sub.4, and the cathode section is doped LiFePO.sub.4. In one embodiment, the SSE is a 5 μm thick layer of LiMPO.sub.4 with a resistance for electrons of 0.5 meg ohms for a surface area of 1 cm2. This resistance is high enough to slow the self-discharge of the battery to an acceptable level for most applications.

(38) In one embodiment, the cathode section is a doped LiFePO.sub.4 material, 100 μm thick, and the SSE section is undoped LiMPO.sub.4, 5 μm thick. With a dense LiFePO.sub.4 material, (approaching 3.6 g/cm3), the capacity of the cathode section is 6 mA-hours per square cm. The self-discharge current is 7.4 μA and the time to self-discharge the capacity of the battery through the SSE would be about 33 days.

(39) Although 33 days is not an exceptional value for the self-discharge time, it is sufficient for many applications, including electric vehicles. Also, LiMPO.sub.4 materials will have lower ion conductivity at low temperatures and may require a warm up before charging or discharging at high rates. Again, this is acceptable for many applications, including electric vehicles. These modest disadvantages are a small compromise in return for an interface between the cathode and SSE that provides excellent mechanical reliability, excellent chemical stability, and excellent ion conductivity, features that are essential to obtain a solid-state battery with high charge and discharge rates.

(40) In other embodiments, the SSE is doped to further reduce its electron conductivity or increase its ion conductivity. In the literature, there is some evidence that small amounts of doping with tri-valent ions like Al.sup.3+, Ti.sup.3+ or Ga.sup.3+ will lower the hole concentration in LiMPO.sub.4, reduce its electrical conductivity, and increase ion conductivity.

(41) However, while there has been much work to make LiFePO.sub.4 and related materials (like LiCoPO.sub.4 or LiMnPO.sub.4) more conductive for application as a cathode, there has been little work to make them less conductive for application as an SSE. In addition, based on the band structure of LiFePO.sub.4 and LiMnPO.sub.4, the measured electron conductivity is very close to that of an intrinsic material, with very few thermally generated carriers, a low mobility, and with existing carriers generated by defects.

(42) In one embodiment, the conductivity for ions in the SSE is improved by perfecting the crystal structure of the small particles from which the continuous material is fabricated, by annealing the compressed and heated powder to form a single crystal, and/or by aligning the b-axis of the crystal or crystallites perpendicular to the surface. Although improved ion conductivity is desirable, other embodiments presented do not require an improvement in either the ion conductivity or a decrease in the electron conductivity in the electrolyte (SSE) section of LiMPO.sub.4 to function adequately.

(43) In one embodiment, as schematically illustrated in FIG. 4 (in cross-section), the anode is lithium metal. During fabrication, all of the lithium is contained within the cathode (401a) and electrolyte (401b) sections of the continuous material. After the battery is assembled and charged, lithium will exit the cathode, move through the electrolyte and plate out on the top surface of the electrolyte (401b). As before, an aluminum substrate (402) was used to make contact to the cathode. Another electrode (402b) is used to make contact to the lithium metal. In one embodiment, this electrode is aluminum. In others, it is an aluminum alloy or another metal or metal alloy that is wet well by lithium. Finally, each island of battery material (cathode, SSE, and anode) is surrounded by a compliant, insulating separator material (407). Lithium wets aluminum well and also wets and diffuses though the thin layer of Al.sub.2O.sub.3 that naturally forms on the surface of the aluminum. In one embodiment, the separator material is a polymer that is also wet well by lithium metal.

(44) It is critical that the lithium metal coats and wets the surface of electrolyte (SSE) uniformly. In the example embodiment discussed above, with a thickness of 100 μm of doped LiFePO.sub.4 material as the cathode and 5 μm of undoped LiMPO.sub.4 as the electrolyte, the storage capacity of the battery is 6 mA-hours per square cm. This is exciting. For a specified total capacity, a smaller area of battery surface is required. Batteries can be lighter and smaller. On the other hand, if the goal for an electric vehicle is to charge to full capacity in 15 minutes, the charging current would 24 mA per sq cm.

(45) A current density of 24 mA per square cm may not seem that high, but for prior-art lithium batteries, this current density is higher than usual. It is especially high for those batteries built with cathodes made from an emulsion of carbon and poorly conducting LiFePO.sub.4 particles in a binder.

(46) In another embodiment, dopants are selected for the cathode section of LiFePO.sub.4 to improve the ion and electron conductivity as much as possible, in order to lower the power dissipation during rapid charging. One could select elements that produced a slightly larger change in lattice parameters during charging and discharging, in return for higher conductivity. Finally, in one embodiment, a smart controller is used to raise the temperature of the battery to 80° C.-100° C., during rapid charging. Both the ion and electron conductivity of LiMPO.sub.4 increase with temperature.

(47) With a high current density, it is especially important to distribute the current uniformly across the top surface of the electrolyte. If the contact between the lithium metal anode and the electrolyte is not uniform, the current can concentrate in small areas and form hot spots. These concentrations of current and hot spots will encourage the electro-migration of lithium into the SSE, especially along any grain boundaries that may exist in a multi-crystalline material. Lithium is extremely light, extremely mobile, and has a low melting temperature (180° C.). It is easily subject to electro-migration.

(48) Electro-migration of lithium metal will form dendrites of lithium metal that can penetrate into an SSE. Hot lithium metal can flow along grain boundaries and into voids and cracks. When the LiMPO.sub.4 material expands or contracts during charge-discharge cycles, the cracks widen and lengthen. Also, lithium expands much more with temperature than LiMPO.sub.4 materials. With temperature cycling, the cracks widen and lengthen. Then, more lithium metal fills the expanded crack and the crack continues to grow. Thus, lithium metal dendrites can steadily crack the SSE material and continue to penetrate until a lithium dendrite contacts the cathode section and causes a short-circuit. A short circuit of lithium metal across the SSE will allow electrons to flow directly into the cathode from the anode, without travelling through the SSE material or the external circuit.

(49) In one embodiment, the cathode and SSE material are deposited in dry nitrogen, and/or heated for hours to drive off any carbonate, hydroxide, or other coatings on the top surface of the SSE. These coatings can interfere with ion conduction and cause hot spots to form. Finally, the clean top surface of the SSE (401b) is exposed to fluorine or HF to form a thin, protective coating of LiF (406). Metallic lithium wets LiF well and a thin layer of LiF will protect the surface of the electrolyte, while offering little resistance to the conduction of lithium ions into the electrolyte.

(50) As above, for the example embodiment of a 100 μm thick cathode material and a 5 μm thick SSE, the battery storage capacity is 6 mA-hours per square cm. With an average discharge voltage of about 3.7 volts, this is an energy storage capacity of 22 mW-hours per square cm. With half of the 10 μm substrate aluminum layer, plus the 10 μm top aluminum layer, the total weight is 0.041 grams/cm2. The energy/weight=0.54 kWh/kg, roughly 86% of the theoretical maximum value for lithium batteries with LiFePO.sub.4 cathodes.

(51) Embodiments of the present invention create a solid-state lithium battery, in which the cathode and SSE are fabricated as a continuous solid material, with no physical separation between them. These embodiments create a lithium battery with excellent reliability and fast charging ability. They solve the fundamental issue of creating mechanically reliable, chemically stable, and highly conducting interfaces between the battery cathode, electrolyte, and anode for a solid-state battery.