WO2016159941A1

WO2016159941A1 - Surface modification of electrode materials

Info

Publication number: WO2016159941A1
Application number: PCT/US2015/023153
Authority: WO
Inventors: Michael Erickson; Konstantin Tikhonov
Original assignee: A123 Systems, LLC
Priority date: 2015-03-27
Filing date: 2015-03-27
Publication date: 2016-10-06

Abstract

A negative electrode active material comprising titanium, for example lithium titanate, includes an inorganic aluminum phosphate surface layer in direct conformal contact. The aluminum phosphate layer may be covalently bound to surface structures of the negative electrode active material. A Li-ion cell comprising the surface-treated electrode active material may provide an improved cycle life and survival at high temperature as compared to Li-ion cells comprising LTO with no surface treatment, wherein the surface layer may form Li_1+xAl_xTi_2-x(PO₄)₃ structures upon battery cycling.

Description

SURFACE MODIFICATION OF ELECTRODE MATERIALS

FIELD OF THE INVENTION

[0001] This application relates to materials and methods for battery electrodes, materials used therein, and electrochemical cells using such electrodes and methods of manufacture, such as lithium secondary batteries.

BACKGROUND AND SUMMARY

[0002] Lithium-ion (Li-ion) batteries are a type of rechargeable battery which produces energy from electrochemical reactions. In a typical lithium ion battery, the cell may include a positive electrode, a negative electrode, an ionic electrolyte solution that supports the movement of ions back and forth between the two electrodes, and a porous separator which allows ion movement between the electrodes and ensures that the two electrodes do not touch.

[0003] Li-ion batteries may comprise metal oxides for the positive electrodes (herein also referred to as a cathode) and carbon/graphite or lithium titanate (herein also referred to as lithium titanium oxide) for the negative electrodes (herein also referred to as an anode), and a salt in an organic solvent, typically a lithium salt, as the ionic electrolyte solution. During charge, the anode intercalates lithium ions from the cathode and during discharge, releases the ions back to the cathode.

[0004] Some catalytic activity of the active materials used in positive and negative electrodes of lithium batteries may have deleterious effects. For example, battery degradation is often a result of electrolyte decomposition that takes place at the anode and/or the cathode, possibly due to the catalytic activity of the active material surface or presence of a specific functional group. The decomposition of the electrolyte results in increased impedance and gas generation, which may lead to degradation of the battery.

[0005] For example, it is believed that metal oxides and mixed metal oxides of nickel, cobalt, aluminum, and/or manganese catalyze oxidation of the electrolyte. Specifically, swelling of lithium nickel aluminum oxide (NCA) pouch cells is believed to be, at least partially, due to the presence of hydroxide groups on the electrode active surface of the pouch cells, causing oxidation of the electrolyte.

[0006] Further, it has been shown that some anode materials, such as lithium titanate (LTO), catalyze the decomposition of the electrolyte. As discussed above, the decomposition of the electrolyte may decrease the useful life of the battery. In addition, the performance of the material or battery may be impaired by traces of moisture. Reducing or fully eliminating this moisture can be beneficial.

[0007] The inventors herein have recognized the above issues and provided a surface- treated electrode active material to address in part the above issues. Provided herein are surface-treated electrode active materials comprising an inorganic aluminum phosphate(AlP04) surface layer directly adjacent to the negative electrode active material wherein the surface layer is covalently bound to the structures on the electrode active materials. An LTO electrode active material, which is fully synthesized, may be mixed with a colloidal suspension comprising precursor materials to the aluminum phosphate. The resultant powder may be dried and heat treated to provide the surface-treated electrode active material which may then be fabricated into an anode for use in a Li-ion cell. The Li-ion cell assembly includes a cathode, the anode comprising the surface-treated electrode active material, a separator, and an electrolyte solution. The Li-ion cell comprising the surface- treated electrode active material may provide an improved cycle life and survival at high temperature as compared to Li-ion cells comprising LTO with no surface treatment. [0008] It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a schematic illustration of a proposed mechanism of solvent reduction on LTO surface.

[0010] FIGS. 2A and 2B are schematics illustrating the surface-treated electrode active material, in accordance with some embodiments.

[0011] FIG. 3 is an example schematic illustrating the formation of a surface layer on LTO to form a surface-treated electrode active material, in accordance with some embodiments.

[0012] FIG. 4 is a schematic example for fabricating an electrode from LTO having a surface layer, in accordance with some embodiments.

[0013] FIG. 5 is a schematic illustration of the intermolecular bonding between LTO and a PVP coating.

[0014] FIGS. 6A and 6B illustrate capacity retention of a Li-ion cell at 40°C and 50°C including an electrode active material having a PVP coating.

[0015] FIG. 7 is an example schematic illustrating the formation of lithium phosphate structures from LTO surface structures and a tri-alkyl phosphate additive, in accordance with some embodiments.

[0016] FIG. 8 is an example method for coating the LTO with AIPO4. [0017] FIG. 9 shows a SEM of the surface-treated electrode active material structures having a surface layer.

[0018] FIGS. 10A-10B shows ion maps of the surface-treated electrode active material.

[0019] FIG. 1 1 shows an example schematic representation of an electrochemical cell.

[0020] FIG. 12 illustrates the capacity retention of a Li-ion cell at 50°C including a surface-treated electrode active material, in accordance with some embodiments.

[0021] FIG. 13 illustrates capacity retention of a Li-ion cell at 60°C including a surface- treated electrode active material, in accordance with some embodiments.

[0022] FIG. 14 illustrates capacity retention of a Li-ion cell over a temperature range including a surface-treated electrode active material, in accordance with some embodiments.

[0023] FIG. 15 illustrates a discharge HPPC test of a Li-ion cell including a surface- treated electrode active material, in accordance with some embodiments.

[0024] FIG. 16 illustrates a regeneration HPPC test of a Li- ion cell including a surface- treated electrode active material, in accordance with some embodiments.

[0025] FIG. 17 illustrates cold cranking at -30°C of a Li-ion cell including a surface- treated electrode active material, in accordance with some embodiments.

[0026] FIG. 18 illustrates a useable energy determination of a Li- ion cell including a surface-treated electrode active material, in accordance with some embodiments.

[0027] FIGS. 19A and 19B are schematic top and side views of a prismatic electrochemical cell, in accordance with certain embodiments.

[0028] FIG. 19C is a schematic representation of an electrode stack in a prismatic electrochemical cell, in accordance with certain embodiments.

[0029] FIGS. 20A and 20B are schematic top and side views of a wound electrochemical cell, in accordance with certain embodiments. DETAILED DESCRIPTION

[0030] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The particular embodiment(s) is merely exemplary in nature and is in no way intended to limit the scope of the invention, its application, or uses, which may, of course, vary. The invention is described with relation to the non-limiting definitions and terminology included herein. These definitions and terminology are not designed to function as a limitation on the scope or practice of the invention but are presented for illustrative and descriptive purposes only. While the processes or compositions are described as an order of individual steps or using specific materials, it is appreciated that steps or materials may be interchangeable such that the description of the invention may include multiple parts or steps arranged in many ways.

[0031] Components, process steps, and other elements that may be substantially the same in one or more embodiments are identified coordinately and are described with minimal repetition. It will be noted, however, that elements identified coordinately may also differ to some degree.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, including "at least one," unless the content clearly indicates otherwise. "Or" means "and/or." As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises" and/or "comprising," or "includes" and/or "including" when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. The term "or a combination thereof or "a mixture of means a combination including at least one of the foregoing elements.

[0033] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0034] The present disclosure provides materials and methods for a surface-treated electrode active material for use in rechargeable batteries to reduce electrolyte degradation, an example degradation mechanism 100 illustrated in FIG. 1, and improve battery performance. The resulting active material structures include inorganic surface layers on the electrode active material, as illustrated in FIGS. 2-3 and 7. The inorganic surface layers may also be referred to as ceramic surface layers. A ceramic is defined as an inorganic compound in regards to the present disclosure. The electrode active material may be treated via reaction with an inorganic solution, an example method is shown in FIG. 8, and then used to prepare electrodes for use in Li-ion cells, as illustrated in FIG. 4. The surface-treated electrode active materials used as an electrode material in Li-in electrochemical cells, illustrated in FIGS. 1 1 and 19-20, showed improved cycle life and survival at high temperature and maintained gassing and cold cranking performance as compared to electrode active material structures which are not treated, illustrated in FIGS. 12-18.

[0035] Surface structures of electrode active material may cause electrolyte decomposition and other unfavorable side reactions when used as an electrode in electrochemical cells. For example, some anode materials, such as lithium titanate (herein also referred to as L TisO^, LTO), may catalyze the decomposition of the electrolyte. Decomposition of the electrolyte may result in gas generation, impedance increase, and therefore decrease the useful life of the battery.

[0036] Turning to FIG. 1 , a schematic illustration of a proposed mechanism of electrolyte decomposition 100 involving hydroxide groups on the electrode active material surface is shown. The hydroxide group catalyzes the removal of !¾ from electrolyte components in this example, decomposing the electrolyte liquid compounds. While this example utilizes lithium titanate, other electrode active materials used in lithium ion batteries may include other proposed mechanisms.

[0037] In some embodiments of this disclosure, surface modification of electrode active materials utilized in lithium-ion batteries are described herein. The treatments disclosed herein are believed to help mitigate undesirable surface modifications of the electrode active material structures through a reaction on the active material surface with battery constituents. One or more solution based compound, for example an inorganic, may be used to react with the surface species of the electrode active material structures to provide a surface-treated electrode active material for use in lithium-ion batteries which improves battery properties.

[0038] Surface layers are configured to be less reactive with electrolyte components than the active material itself. In other words, a surface layer reduces the reactivity of electrode active material to which the surface layer is bound. To illustrate this difference in reactivity, reaction mechanisms, such as illustrated in FIG. 1 above, will now be briefly described for typical active materials and electrolyte components. Without wishing to be bound by a particular theory, it is believed that metal oxides of nickel, cobalt, aluminum, titanium, and manganese can catalyze decomposition of electrolyte components and electrolyte solvents. For example, carbonates, such as ethylene carbonate (EC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), and solvents that are commonly used for battery electrolyte, can oxidize on the surface of many metal oxides at high potentials (e.g., greater than 4.0V, 4.5V or 5.0V). Such potentials are common for many positive electrodes. In one example, lithium titanate, which is used for negative electrodes, includes oxide and hydroxide groups. At the same time, hydroxide groups of lithium titanate may undergo a reduction and release of hydrogen, as illustrated in FIG. 1 , which goes into the gas phase. Other electrode active materials are often imparted by surface species that introduce undesirable effects in the functioning or fabrication of the battery.

[0039] In addition, the performance of the material and/or battery may be impaired by traces of moisture. Reducing or fully eliminating this moisture may be beneficial. For example, a surface layer formed on electrode active materials may increase hydrophobicity of the structures. As a result, the structures may have less attraction towards water and adsorb less moisture from the environment when stored as a powder (raw materials) for the fabrication of electrodes, as part of a partially of fully assembled electrode, and/or as part of a dry cell assembly.

[0040] Referring to FIGS. 2A and 2B, example schematics illustrating the surface-treated electrode active material 200 and 210, in accordance with some embodiments are shown. In this example, a surface-treated electrode active material 200 is shown wherein a negative electrode active material 204 is lithium titanate and a surface layer 202, formed from a colloidal suspension including an inorganic A1P0_4; is covalently bound to the surface structures of the active material. In some examples, the surface layer may be formed from A1P0₄, AIF3, or AI2O3. The lithium titanate 204 includes a plurality of lithium titanate particles. For example, the lithium titanate 204 may be present as a secondary particle comprising a plurality of primary particles. In one example, the lithium titanate 204 may be synthesized from precursor materials. In another example, the lithium titanate 204 may be pre-synthesized. It should be noted that the provided active material is an electrode active material which may be used to fabricate an electrode with no further treatment and/or synthesis steps. The surface layer 202 may comprise more than one structure, as illustrated in FIG. 2B. For example, the surface layer may further comprise L1₃PO4 208 and Lii_+xAl_xTi₂- _Χ(Ρ0₄)3 206 structures. In other examples, other composite structures may be present depending on the materials including at the various processing steps, an example described in FIG. 4.

[0041] The disclosed treatments may help overcome unwanted side reactions between the electrolyte and the electrode active material, for example as described at FIG.1, by forming a surface layer on the electrode active material structures, thereby preventing or at least minimizing direct contact between the surface of the electrode active material and an electrolyte. The surface layer operates as a barrier between the active material and the electrolyte. As a result, a less reactive surface of the electrode active material is exposed to the electrolyte instead of the more reactive surface structures of the electrode active material.

[0042] A surface layer may be formed when the electrode active materials are combined with a liquid to form a mixture. For example, FIG. 3 shows an example schematic 300 illustrating the formation of an inorganic A1P0₄ surface layer on an electrode active material, for example, LTO. The LTO 302 is mixed with the surface reagent, in this example a colloidal suspension of A1P0₄, wherein the inorganic may include precursor materials. The surface layer 304 of inorganic A1P0₄ may be covalently bound to surface of the negative electrode active material, illustrated as LTO 306. This feature helps to maintain the surface layer on the surface of the electrode active material when, for example, the structures are subjected to further processing, such as electrode fabrication, or under operation, such as lithiation and delithiation. Upon lithiation, the A1P0₄ surface layer covalently bound to LTO may react to form a Lii_+xAl_xTi₂-_x(P0₄)3 structure 308, consuming some of the lithium present in the Li-ion cell, illustrated as LTO 312. In some examples, there may be some L1₃PO4 structures 310. In some other examples, there may remain some inorganic A1P0₄ on the LTO surface following a charge/discharge cycle of a Li-ion battery. Thus, the AIPO4-LTO coating upon lithiation may produce a mix of structures covalently bound to the LTO surface. The formation of the Lii+_xAl_xTi2-_x(P04)3 type compounds during lithiation, also referred to as cell formation, is unique to the LTO active material as the titanium is a critical structural element needed for the surface coating durability. For example, other active materials, such as LMO, NCM, NCA, and LCO, cannot contribute titanium and thus will not form Lii_+xAl_xTi2-_x(P0₄)3 compounds.

[0043] In some examples, the mixture may include one or more surface reagents. The surface reagents may be part of the liquid that is combined with the structures or added into the mixture after the structures are combined with the liquid. The electrode active material may be provided as a fully synthesized powder (for example, the electrode active material may be ready for use in an electrode). For example, the fully synthesized powder may comprise secondary particles having primary particles. For example, negative electrode active materials may be provided fully synthesized as a powder and treated in a resultant mixture to form a surface layer. The surface-treated electrode active material may then be extracted from the resultant mixture and be used to fabricate an electrode.

[0044] Without being restricted to any particular theory, removal or blocking of hydroxide groups of the surface of electrode active material structures with a less reactive surface layer is believed to be one mechanism for reducing decomposition and/or reduction of electrolyte. Another mechanism is deactivating the lithium metal oxide surface reactivity. Electrochemical cells assembled with surface-treated electrode active materials demonstrate improved performance in comparison to cells assembled with untreated electrode active material materials as described herein. For example, the cells assembled with the surface- treated electrode active material demonstrated increased cycle life, stability towards electrolytes, stability at high temperatures (e.g. 50°C, 60°C, 75°C or 85°C), and maintained performance during cold cranking.

[0045] Furthermore, surface-treated electrode active material may also decrease metal dissolution of the active material, reduce catalytic activity towards the electrolyte, and thereby achieve a corresponding reduction in parasitic reactions and self-discharge. A stable interface between the electrode active material and the electrolyte may also result in improved durability in terms of crystal structure breakdown. If a surface of untreated electrode active material is exposed to electrolyte, the metal from the metal oxide may dissolve/leach out. This, in turn, may affect the crystal structure of the active material on the surface. However, surface-treated electrode active material tends to be more stable.

[0046] Referring now to FIG. 4 an example schematic 400 for fabricating an electrode from an electrode active material, such as LTO, is shown. The example shown uses LTO as the electrode active material and inorganic AIPO4 for surface treatment. The provided surface-treated electrode active material provides an electrode material for use in Li-ion batteries, which is capable of increasing cycle life.

[0047] Forming surface-treated electrode active materials may be performed prior to using the electrode active materials for fabricating the electrodes and cells, as described below with reference to FIG. 4, following fabricating the electrode active materials. The stage at which the surface layers may be formed is important as different kinds of surface layers may be produced. Surface layers can be fabricated on the materials during material manufacturing process: as the active materials are being made from the precursors, before, after or during the heat treatment of the particles following the synthesis. In some embodiments, other surface layers may be created during the slurry preparation and heat the materials are exposed to during electrode coating. In other embodiments, yet other layers may be created after the cells are assembled by exposing the active material structures to reactive gas or liquid. Finally, surface layers can be produced after cell assembly through a reaction of the active materials with electrolyte components: salts, solvents and additives. For purposes of this disclosure, forming surface layers on electrode active material structures may also be referred to as surface treatment of the electrode active material structures. These specific surface layers are covalently bound to the electrode active materials structures. As such, the type of surface treatments as described herein should be distinguished from other surface treatments when, for example, surface layers are not formed or newly formed surface layers are not covalently bound to the electrode active material structures. Thus, a physical coating would not be considered a surface treatment or surface layer as outlined in the current application.

[0048] Turning to FIG. 4 at 402, the electrode active material may be obtained. In this example, the electrode active material is shown as lithium titanate, LTO. In other examples, the electrode active material may be another metal oxide active material capable of lithiation and delithiation. In yet another example, the electrode active material may comprise titanium. The obtained electrode active material may be present in a form ready for fabrication into an electrode. For example, the electrode active material may be present as secondary particles comprising primary particles of the electrode active material. In some embodiments, the electrode active material may present in the form of a powder or as particulates. In some embodiments, the electrode active material primary particles are loosely associated with each other and the secondary particles are largely not present. Primary particles of the electrode active material can be less than Ι μηι in size or less than 0.5μηι in size. Secondary particles can be about Ι μηι, or 5μηι or 7.5μηι or ΙΟμηι. Larger secondary particles may be easier to process and have smaller active surface area. Smaller surface area may result in less degradation over time. Smaller secondary particle sizes have a benefit of a shorter diffusion path and higher rate capability. In some embodiments, the electrode active material is doped with metals such as molybdenum, zirconium or others, or is doped with carbon or carbon nanotubes to increase its electronic conductivity.

[0049] In one example, the electrode active material may optionally include a preliminary surface treatment 430. For example, the preliminary surface treatment 430 may be done to minimize the reaction of LTO with water and reduce the formation of LiOH on the surface. In one example, the preliminary surface treatment may be done using silanes, such as oxy- silanes. In another example, the preliminary surface treatment may include heat treating the electrode active material to remove surface groups and impurities. For example, the heat treating may be done at 200°C to 800°C under vacuum, or in air, or in gas (e.g. nitrogen or argon). In yet another example, the preliminary surface treatment may include coating the electrode active material with a polymer which may be made into a carbon coating, for example using pyrolysis.

Proceeding from 402, the electrode active material may receive the surface treatment to form a surface-treated electrode active material. For example, the surface treatment may be an inorganic AIPO4 layer on LTO 406. Alternatively, the electrode active material may be used to fabricate an anode for use in a Li-ion cell with no surface treatment. Thus, the provided electrode active material may be used without the surface treatment in accordance with the disclosed embodiments, for example, to prepare a control cell with an uncoated LTO anode.

[0050] Referring back to 402, the provided electrode active material may be treated to form a surface-treated electrode active material, as described in FIGS. 2 and 3 above. The electrode active material 402 may be mixed with a colloidal inorganic AIPO4 solution 404 to surface treat the LTO with the inorganic AIPO4 (herein also referred to as AIPO4) in order to provide the surface-treated electrode active material 406. The AIPO4 colloidal solution 404 may be prepared using Al and PO4 precursor materials. The surface-treated LTO active material may then be fabricated into an anode at 408. [0051] In some examples, the precursor materials may comprise water soluble salts. In one embodiment, a salt comprising a phosphate anion and a salt comprising an aluminum cation may be used. In some embodiments, one or more water soluble salts may be included. The water soluble salts may be chosen to have a pH that is neutral, e.g. pH of 7, or greater than neutral, e.g. pH > 7, and thus may not react with LTO, which typically has a pH >9. For example, the precursor materials may form A1P0₄, wherein the precursor materials may be A1(N0₃)3*9H₂0 and (NFU^HPC^. In another example, the inorganic precursor materials may form AIPO4, wherein the inorganic precursor materials may be Α1(θ2¾θ2)3 and K3PO4.

[0052] At 408, the surface-treated electrode active material, for example an AIPO4 surface-treated LTO active material, may be fabricated into an anode and may include other processing steps. For example, the anode may include active materials and a current collector. In some embodiments, the anode may comprise either a metal selected from the group consisting of Li, Si, Sn, Sb, Al, and a combination thereof, or a mixture of one or more anode active materials in particulate form, a binder (in certain cases a polymeric binder), optionally an electron conductive additive, and at least one organic carbonate. Examples of useful anode active materials include, but are not limited to, lithium metal, carbon (graphites, coke-type, mesocarbons, polyacenes, carbon nanotubes, carbon fibers and the like). Anode- active materials also include lithium-intercalated carbon, lithium metal nitrides such as Li₂.₆Coo.4N, metallic lithium alloys such as LiAl, Li₄Sn, or lithium-alloy-forming compounds of tin, silicon, antimony, or aluminum. Further included as anode-active materials are metal oxides such as titanium oxides, iron oxides, or tin oxides.

[0053] For example, fabricating the electrode may include several suboperations such as mixing the LTO electrode active material into a slurry, coating the slurry onto a conductive substrate, drying the coating, compressing the coating, and calendaring. In one example, the slurry may be coated on both sides of the current collector. In another example, the slurry may be coated on one side of the current collector. Further, the slurry may comprise nonaqueous liquids, and additives, such as a binder or a conductive additive.

[0054] Suitable binders may include, but are not limited to, polymeric binders. For example, a polymer binder selected from the group consisting of polyacrylonitrile, poly(methylmethacrylate), poly(vinyl chloride), polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropene), polyacrylic acid, styrene butadiene rubber, carboxymethylcellulose and copolymers thereof.

[0055] In some embodiments, slurry additives 432 may be optionally incorporated into the slurry which treats the electrode active material. In one example, the slurry additive may comprise silanes added to the slurry, which may chemically react and form a covalently bound silane surface layer to the electrode active material structures. The silanes may reduce the reactivity of the electrode active material structures with respect to the electrolyte. For example, the silane may be an oxy-silane.

[0056] In one embodiment, oxy-silane may be added to the slurry. For example, a typical positive electrode was prepared using lithium manganese oxide (LMO), Super P, KS6 graphite, and PVDF. A matching negative electrode was fabricated using a slurry formed from LTO powder (available from Hanwha in Seoul, South Korea), KS6 graphite, Super P, PVDF, and N-Methyl-2-pyrrolidone. Prior to introducing a surface reagent, the slurry had 45% solid content. After mixing and final degas of the slurry (i.e., at the state when slurry is typically ready for coating), MTMS (Dynasylan MTMS available from Evonik Industries in Essen, Germany) was added to the slurry in an amount equal to 1% by weight based on the weight of LTO. The slurry was stirred to dissolve the MTMS in the NMP. Thin film coatings were cast on both sides of 16micrometer thick aluminum foil. Each side had a loading of 10 mg/cm². The coating film was then compressed to a density of 1.8 g/cm3. A control LTO negative electrode, which did not have any MTMS added, was also prepared in an otherwise similar manner. The same positive electrode was used for both silane treated LTO cells and control cells.

[0057] Electrodes having a size of about 50 mm by 80 mm were punched from the pressed coated sheets. An uncoated strip of foil extended along one side of the electrode and used to attach tabs. The electrodes were then dried for 16 hours under a vacuum at 125°C. The electrodes were then arranged into stacks with a 20 micrometer thick polyethylene separator (available from W-Scope in Chungcheong-Do, Korea) and sealed in a laminated aluminum foil pouch. Each stack was disposed in a separate rectangular pouch with one side open and dried under a vacuum at 60°C for 48 hours. The cells were then filled with electrolyte having the following formulation: 1 M LiPEe / PC:EMC at a ratio of 1 :4. The cells went through C/10 charge/discharge cell formation cycling with 1.5V and 2.7 V used as cut-off voltages, and were then vacuumed and sealed. The average cell impedance for the control cells (fabricated with the untreated LTO) was 42 mOhm, while the average cell impedance for the silane treated LTO cells (with the silane treated LTO) was 43 mOhm.

[0058] After these fabrication operations, the control cells and the silane treated LTO cells were subjected to cycle life testing at 50°C and 60°C to compare cycle life and stored at 60°C and 100% state of charge (SOC) to compare swelling and impedance changes. The cycle life data for the two types of cells cycled at 50°C for about 500 cycles show that even after a few initial cycles, the silane treated LTO cells (with the silane treated LTO) showed superior performance in comparison to the control cells (fabricated with the untreated LTO). The capacity retention was almost 5% greater for the silane treated LTO cells during most of the cycling test. The difference in performance was even more profound at higher temperatures. Specifically, the cycle life data for the same two types of cells cycles at 60°C. At about 175 cycles, the capacity retention of the controlled cells fell below 50%, while the capacity retention of the silane treated LTO cells stayed at about 65%. Cycling was performed at a rate of 1 C charge with+ 2. 7 V CVC with C/20 cutoff and a rate 1 C discharge with 15 minute rests between charges and discharges.

[0059] As noted above, in the storage test, after cell formation cycling, the silane treated LTO cells (with the silane treated LTO) and the control cells (fabricated with the untreated LTO) were charged to 100% SOC and stored at 60°C for about 60 days. The thickness of the cells and capacity retention were monitored for these cells. The control cells doubled their thicknesses (on average) after about 23 days of such storage, while the silane treated LTO cells have never reached this level of the thickness increase, even after 60 days of storage. Further, the capacity retention for the same two types of cells after different storage durations were studied. The cells were discharged to 1.5 V from 100% SOC at the C/5 rate, and charged to 2. 7 V at the C/5 rate followed by the discharge to 1.5 Vat the C/5 rate. Subsequently, the cell was recharged to 2.7 V, 100% SOC for additional storage. The capacity retention was about 10% better for the silane treated LTO cells in comparison to the control cells. Overall, both swelling and capacity retention characteristics have improved with introduction of silane treatment of LTO.

[0060] In another embodiment, MTMS may be used to treat LTO while it was still in the powder form and prior to combining LTO structures with a polymer binder. This treatment is different from the one in the above described experiment, where MTMS was introduced into the slurry. The mechanism of forming a surface layer covalently bound to the LTO structures is believed to be the same.

[0061] Before introducing the LTO into a slurry mix, the LTO powder was treated with MTMS. Specifically, the LTO powder, ethanol, and water were mixed together according to the following weight ratio of 1 :3:0.01 for LTO: ethanokwater. Continuous mixing was used to keep the LTO particles constantly suspended. MTMS was added drop-wise so that a weight ratio of LTO:silane was 100: 1. This mixture was stirred for 30 minutes. The powder was then filtered and washed twice with ethanol and finally dried for 16 hours at 120°C under vacuum. Infrared spectroscopy results for this silane modified LTO powder illustrate a peak corresponding to the C-H bond typically found in methyl groups. The same peak was found for the MTMS sample, but not for the untreated /baseline LTO.

[0062] In this second experiment, fabrication of positive and negative electrodes was similar to the test cells used in the first experiment. The only difference was that no MTMS was added to the negative slurry. After cell formation cycling, the control cells (without any LTO silane treatment) and the silane treated LTO cells (with the LTO silane treatment of the powder) were subjected to cycle life testing at 60°C to compare cycles. Similar to the results described above, the capacity retention of the controlled cells fell below 50% after about 175 cycles. However, the capacity retention of the silane treated LTO cells stayed at about 60%. It should be noted that when silane treatment was performed by adding MTMS into slurry, the results were slightly better. As described above, the capacity retention of the silane treated LTO cells fell with LTO structures treated at the slurry stage was about 65% after about 175 cycles.

[0063] In another experiment, a high molecular weight silane (Evonik 91 16 available from Evonik Industries in Essen, Germany, molecular weight 346.62 g/mol) was added to the LTO powder in attempt to form a surface layer similar to the one formed with MTMS. For reference, the molecular weight of MTMS in the previous experiment was 136.22 g/mol. The treatment of the LTO powder was performed in a manner similar to MTMS treatment of the LTO powder described above. However, the silane treatment did not show any improvement in cycle life or swelling in comparison to the controlled cells. Without being restricted to any particular theory, it is believed that dry blending of treated powders causes mechanical scarping of surface layers previously formed on the electrode active material structures when these structures hit each other. [0064] In another embodiment, the slurry additive 432 may comprise poly (vinylpyridine) (PVP) 502, which may interact with hydroxyl groups on the surface of the electrode active material 504 through intermolecular forces 506 such as hydrogen bonding and dipole-dipole bonding. PVP is a polymer which may interact with LTO via intermolecular forces, as illustrated in example schematic 500 in FIG. 5.

[0065] The addition of PVP to the slurry prior to the electrode coating process may be done in n-methyl-pyrrolidone (NMP), a solvent which is commonly present in slurries, as PVP is soluble in NMP. Once the NMP is removed during coating, the PVP coats the electrode active material surface structures to form a monolayer. The monolayer interaction of the PVP and the electrode active material surface structures should be fairly strong due to the presence of intermolecular forces, such as the hydrogen bonding. This method of in-situ slurry additive for coating a LTO surface with PVP has minimal impact on the manufacturing process in comparison, for example, to other methods of surface coating where powders are coated in a separate process and then introduced to the slurry. This simpler addition decreases the number of process steps and associated costs with added processes. In one example, electrodes with the PVP slurry-coated LTO may be prepared using lwt. % PVP per LTO. 0.8 Ah cells were fabricated comprising an electrode with the PVP slurry-coated LTO with a matching lithium manganese oxide cathode. Cells were cycled at 40°C, FIG. 6A, and 50°C, FIG. 6B, and compared with the exact same cell design but built with bare LTO (no coating) containing anode, 604 and 608 respectively. In both 40°C and 50°C cycling, the PVP-LTO 602 and 606 cycled with less fade in comparison to bare LTO.

[0066] Two cells were made with bare LTO and two cells were made with the PVP-LTO. They were then charged to 100% SOC and stored at 50°C for 28 days. The cell with bare LTO swelled 43% in thickness, while the cell the PP-LTO increased in thickness by 40%, included in Table 1 below. TABLE 1 :

[0067] For example, a slurry additive 432 may be optionally included, as previously described. In one example, the surface-treated active material may be mixed with a binder and at least one additive in a non-aqueous solvent to form a slurry which is coated onto a current collector. The coated current collector may then be dried and calendared to form the anode comprising the surface-treated electrode active material. In some embodiments, the anode may receive the gaseous treatment 434 as described above. The anode comprising the inorganic A1P0₄ surface-treated LTO anode may then be fabricated into a Li-ion cell as illustrated at 418, wherein the Li- ion cell may include a cathode 410, a separator 412, and the anode comprising the surface-treated electrode active material 414. In some embodiments, the Li-ion cell may receive the gaseous treatment 434.

[0068] In one embodiment, a gaseous treatment 434 may be performed on the anode following fabrication and drying. In another embodiment, the gaseous treatment 434 may be performed following fabrication of the Li-ion cell and drying, directly prior to filling with electrolyte. In yet another embodiment, the gaseous treatment may not be performed on the anode. The gaseous treatment exposes the available surfaces of the electrochemically active material which are accessible to gaseous reactants to produce the modified surface having improved properties for use in the lithium battery. In one example, the gaseous reactant may have a molecular weight of about 300 g/mol or less. For example, the gaseous reactant may be selected from the group consisting of hydrides, oxides, sulfides, oxysulfides, fluorides, and oxyfluorides of carbon, sulfur, phosphorus and boron. In other example, a mixture of two or more gaseous reactants may be used. The gaseous reactant may chemically modify the surface of the electrochemically active material that is accessible to the gaseous reactant, thereby producing a modified electrochemically active material having improved properties for use in the Li-ion battery.

[0069] Thus, a Li-ion cell comprising a surface-treated electrode active material may be provided at 418.

[0070] For example, the cathode may be formed by mixing and forming a composition comprising a binder, a conductive additive, solvent, etc. to prepare a slurry wherein the slurry is then coated on a substrate, e.g., a current collector which is then followed by drying to produce the electrode. Further, such electrode materials may be subjected to roll forming or compression molding to be fabricated into a sheet or pellet, respectively.

[0071] In other examples, the cathode active material, herein also referred to as the positive electrochemically active material or the positive electrode active material, is a lithium transition metal phosphate compound having the formula (Lii__xZ_x)MP04, where M is one or more of vanadium, chromium, manganese, iron, cobalt, and nickel, Z is one or more of titanium, zirconium, niobium, aluminum, tantalum, tungsten or magnesium, and x ranges from 0 to 0.05 or Lil-xMPC^, wherein M is selected from the group comprising vanadium, chromium, manganese, iron, cobalt, and nickel; and 0 < x < 1.

[0072] In yet another example, the positive electrochemically active material is a lithium metal phosphate, for example, lithium iron phosphate. The positive electrochemically active material may be present as powder or particulates with a specific surface area of greater than 5 m²/g, 10 m²/g, or greater than 15 m²/g, or greater than 20 m²/g, or even greater than 30 m²/g. [0073] For example, the cathode may comprise a lithium metal phosphate. In one example, the lithium metal phosphate may be lithium iron phosphate, LiFeP0₄. Further, the LiFeP0₄ may have an olivine structure and be made in the form of very small, high specific surface area particles which are exceptionally stable in their delithiated form.

[0074] The separator has no particular restriction on the source material or morphology of the separator for the Li-ion cell. Additionally, the separator serves to separate the anode and the cathode so as to avoid their physical contact. The preferred separator has higher porosity, excellent stability against the electrolytic solution, and excellent liquid holding properties. Example materials for the separator may be selected from nonwoven fabric or porous film made of polyolefins, such as polyethylene and polypropylene, or ceramic coated materials.

[0075] The Li- ion cell may then be filled with electrolyte 416 (indicated by the hashed lines), to produce a filled Li-ion cell 420. The electrolyte 416 is in intimate contact with the components in the Li-ion cell, as illustrated. The electrolyte may comprise Li salt, organic solvents, such as organic carbonates, and additives. The electrolyte is present throughout the Li-ion cell and in physical contact with the anode, cathode, and separator. The molar concentration of the lithium salt may be between 0.5 and 2.0 mol/L.

[0076] Further, the electrolyte may comprise aprotic solvents. For example, the solvent may comprise at least one of cyclic carbonates and linear carbonates. Some examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethylvinylene carbonate, vinylethylene carbonate, and fluoroethylenecarbonate. In some examples, the cyclic carbonate compounds may include at least two compounds selected from ethylene carbonate, propylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate. Some examples of linear carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate and dibutyl carbonate. The alkyl group of the linear carbonates can have a straight or branched chain structure. Some examples of other electrolyte solvents include lactones such as γ-valerolactone, γ- butyrolactone, alpha-angelica lactone; nitriles such as acetonitrile and adiponitrile; linear esters such as methyl acetate, methyl propionate, methyl pivalate, butyl pivalate, hexyl pivalate, octyl pivalate, dimethyl oxalate, ethyl methyl oxalate, and diethyl oxalate; amides such as dimethylformamide; compounds having an S=0 bonding such as glycol sulfite, propylene sulfite, glycol sulfate, propylene sulfate, divinyl sulfone, 1,3-propane sultone, 1,4- butane sultone, and 1 ,4-butanediol dimethane sulfonate; other solvents such as tetrahydrofuran, 2-methyl tetrahydrofuran, tetrahydropyran, dimethoxyethane, dimethoxymethane, ethylene methyl phosphate, ethyl ethylene phosphate, trimethyl phosphate, triethyl phosphate, halides thereof, and, poly(ethylene glycol), diacrylate, and combinations thereof.

[0077] Examples of combinations of the non-aqueous solvents include a combination of a cyclic carbonate and a linear carbonate; a combination of a cyclic carbonate and a lactone; a combination of a cyclic carbonate, a lactone, and a linear ester; a combination of a cyclic carbonate, a linear carbonate, and a lactone, a combination of a cyclic carbonate, a linear carbonate, and an ether; and a combination of a cyclic carbonate, a linear carbonate, and a linear ester. Preferred are the combination of a cyclic carbonate and a linear carbonate, and the combination of a cyclic carbonate, a linear carbonate and a linear ester.

[0078] The lithium salt may be selected from a group consisting of LiC10₄, L1PF6, L1BF4, L1SO3CF3, LiN(CF₃S0₂)(C4F₉S0₂), LiBOB, LiTFSi, lithium salts including a chain fluorinated alkyl group such as LiN(CF₃S0₂)₂, LiC(CF₃S0₂)₃, LiN(CF₃CF₂S0₂)₂, LiPF₄(CF₃)₂, LiPF₃(C₂F₅)₃, LiPF₃(CF₃)₃, LiPF₃(iso-C₃F₇)₃ and LiPF₅(iso-C₃F₇), lithium salts including a cyclic fluorinated alkylene group such as LiN(CF₃S0₂)₂ and LiN(CF₃)₃(S0₂)₂. [0079] The electrolyte salt can be used singly or in combination. Examples of the preferred combinations include a combination of LiPF₆ with L1BF4, a combination of L1PF₆ with LiN(S02CF3)2, and a combination of L1BF4 with LiNSC CFs^. Most preferred is the combination of LiP₆ with L1BF4, though again, these preferential combinations are in no way limiting. There is no specific limitation with respect to the mixing ratio of the two or more electrolyte salts. In the case that L1PF₆ is mixed with other electrolyte salts, the amount of the other electrolyte salts preferably is about 0.01 mole % or more, about 0.03 mole % or more, about 0.05 mole % or more based on the total amount of electrolyte salts. The amount of the other electrolyte salts may be about 45 mole % or less based on the total amount of the electrolyte salts, about 20 mole % or less, about 10 mole % or less, or about 5 mole % or less. The concentration of the electrolyte salts in the non-aqueous solvent may be about 0.3 M or more, about 0.5 M or more, about 0.7 M or more, or about 0.8 M or more. Further, the electrolyte salt concentration preferably is about 2.5 M or less, about 2.0 M or less, about 1.6 M or less, or about 1.2 M or less.

[0080] In some embodiments, the electrolyte may comprise an electrolyte additive 436. For example, inorganic or organic electrolyte additives may be included in the electrolyte. In one example, an inorganic metal salt additive may be included which acts as a barrier between the electrode active material and the electrolyte. For example, the multivalent metal salt may contact the electrochemically active material structures and form a treated surface which operates as a barrier between the active material and other electrolyte components. The multivalent metal salts may include one of the following multivalent metal ions: Ba, Ca, Ce, Co, Cu, La, Mg, Mn, Ni, Nb, Ag, Ti, Al, Zn, Ur, Pb, Fe, Hg and Gd. The metal ions may be selected based on their reduction potential vs. lithium. For example, the multivalent metal ions may form covalent bonds with oxygen sites available on the surface of the active materials. [0081] In another example, electrolyte additives may be included which would form secondary layers on the Lii_+xAl_xTi₂-_x(P0₄)3 structures (which form during cell formation of the battery, described below). In one example, vinylene carbonate (VC) and other organic SEI formers (maleic anhydride, succinic anhydride) may be added to the electrolyte. These additives may be beneficial to create secondary, organic films, polyalkyl containing films on the electrode active material structures thereby protecting them from partial dissolution in the electrolyte at elevated temperatures. In another example, sulfur-containing (e.g. LiTFSI, PS) and fluoride-containing (e.g. FEC, fluorinated carbonates) additives may be added to the electrolyte. These sulfur-containing and fluoride-containing additives may be beneficial for creating insoluble inorganic films on the surface of the electrode active material structures to protect the structures from further direct interactions with electrolyte solvents. In yet another example, the electrolyte additive may be a tri-alkyl phosphate-based additive 440, such as trioctylphosphate (TOP, C₂4H₅i0₄P).

[0082] The Li-ion cell filled with electrolyte 416 may then undergo cell formation, referred to also as a first charge/discharge cycle, to form Li-ion cell 422. During cell formation, the electrolyte reacts with the anode comprising the surface-treated electrode active material to form a solid electrolyte interface (SEI) layer. Further, during cell formation other reactions, for example additive reactions, may occur. In some embodiments, heat treatment 438 of the Li-ion cell during cell formation may be performed. Heat treatment 438 may affect the kinetics of the battery components reactions. For example, the cells may exposed to temperatures between 30°C to 100°C, such as 35°C, 45°C, 60°C, 80°C, or 100°C, for a period of time between 30 minutes to 7 days. The additional exposure of the cells may allow the inorganic A1P0₄ LTO materials to react and form the surface structures 424. The electrolyte additives may react to form additional structures during cell formation and addition exposure to temperature, as described above. [0083] The inorganic AIPO4 treated LTO Anode phase may convert to a Lii_+xAl_xTi2- _Χ(Ρ0₄)3 structure upon operating a lithium ion cell, cell formation. Among lithium ion active materials, formation of Lii+_xAlxTi2-_x(P0₄)3 structures is unique to LTO, with titanium being a critical structural element needed for surface coating durability. Other active materials may be unable to contribute titanium and as such will not form Lii_+xAl_xTi2-_x(P0₄)3 structures.

[0084] In one embodiment, the non-aqueous electrolyte further comprises an additive to enhance the Lii_+xAl_xTi2-_x(P0₄)3 structures. For example, the additive may be a tri-alkyl phosphate. In one example, the additive may be trioctylphosphate.

[0085] Turning to FIG. 7, example schematic 700, illustrating the surface-treated electrode active material 710, for example LTO with an inorganic -AIPO4 surface layer 702 with the addition of a tri-alkyl phosphate electrolyte additive, is shown. For example, the electrolyte additive being a tri-alkyl phosphate-based additive, such as trioctylphosphate (TOP, C24H₅1O4P), may be added to the electrolyte to form additional surface layers, i.e. structures, during cell formation, for example lithium phosphate and lithium polyphosphate (L13PO4, and LiO(P03)Li, etc.) which intermix with the structures formed from the AIPO4/LTO phase 712. Without wishing to be bound by a particular theory, the additional lithium phosphate surface layers 706 are thought to be formed as a result of the hydrolytic reaction of LiOH on the surface of LTO, as illustrated in reaction 1, wherein water reacts with basic LTO to form the LiOH, with the tri-alkyl phosphate -based additive eventually resulting in completely hydrolyzed phosphate and alcohols, as illustrated in FIG. 7 and reactions 1 , 2, and 3 below.

LTO + H₂0 → LTO + LiOH s, urface (1)

C₂₄H₅₁0₄P _^ι1™ Li₃P0₄ + 3HOC₈H₁₇ (2)

Li₃P0₄ + AIP0₄ → Li_1+xAl_xTi₂__x(P0₄)₃ (3) These lithium phosphate compounds have been studied in the chemical literature as ion conductors and are ionically conductive, for example when present as a very thin layer, e.g., a monolayer. The additional phosphate structures may form an enhanced surface layer 706 which may further inhibit catalytic degradation mechanisms and improve the durability of the LTO-electrolyte interface in combination with the Lii_+xAl_xTi2-_x(P0₄)3 structures 704. The addition of the tri-alkyl phosphates may reduce the presence of LiOH on the surface of the LTO through the L1₃PO4 and alcohol formation, illustrated in reaction 2. LiOH, as described in regards to FIG. 1 , degrades electrolyte components. For example, the tri-alkyl phosphates may be added from 0.1 to 5 wt. % to react with surface LiOH groups. In some examples, tri- alkyl phosphates may be in excess and remain unreacted. It should be noted that excess unreacted tri-alkyl phosphates does not create risk to cell performance and may reduce flammability as tri-alkyl phosphates are a flame retardant. The additive enhances the surface layer and covalently bonds to the negative electrode active material structures. The tri-alkyl phosphate-based additive may be added to enhance the surface layer as well as provide benefits to the cell regarding flammability. The surface-treated electrode active material may further comprise AIPO4 and L13PO4 structures as part of the surface layer of the negative electrode active material.

[0086] As described in FIG. 4, a lithium ion battery may be fabricated wherein the surface-treated electrode active material is used to prepare an anode. The lithium ion battery may include a cathode, a separator, an electrolyte, and the anode. The anode may comprise the surface-treated electrode active material. The surface-treated electrode active material may be prepared by receiving the negative electrode active materials, wherein the negative electrode active materials are lithium titanate. A colloidal solution comprising inorganic precursors, for example A1(N0₃)3*9¾0 and (NH₄)₂HP0₄, for AIPO4 is prepared and then the negative electrode active materials are mixed into the prepared colloidal solution to form a resultant mixture. The resultant mixture may be dried and then heat treated to obtain the surface-treated electrode active material wherein the surface-treated electrode active material comprises a surface layer of inorganic, for example as illustrated in FIG. 3 above. A slurry may then be prepared using the surface-treated electrode active material wherein the slurry is configured for coating onto a current collector. Coating the slurry onto the current collector followed by drying, forms an anode for use in a lithium ion cell. Upon operating a lithium ion cell containing an anode comprising the surface-treated electrode active material, the AIPO4-LTO phase may convert to a Lii+_xAl_xTi2-_x(P04)3 structure. Thus, a method for a surface-treated negative electrode active material, for example LTO, is provided for use in a lithium ion cell.

[0087] Method 400, for example, may provide a surface-treated electrode active material for use in a lithium ion battery. The surface-treated electrode active material may comprise a negative electrode active material for intercalating and deintercalating lithium ions comprising titanium. For example, the negative electrode active material may be lithium titanate. The negative titanium electrode active material may comprise an inorganic AIPO4 surface layer wherein the inorganic AIPO4 surface layer is directly adjacent to the negative titanium electrode active material. Upon a charge/discharge cycle in a Li-ion cell, Lii_+xAl_xTi₂-x(P0₄)3 structures may form, which are unique to titanium comprising active material. The inorganic AIPO4 surface layer may be covalently bound to the surface structures of the negative electrode active material. The inorganic AIPO4 surface layer may be less than ΙΟμηι. For example, the inorganic AIPO4 surface layer may have a range of 0.5μηι to ΙΟμηι. The surface-treated electrode active material may be used in a lithium ion battery.

[0088] Further, in accordance with some embodiments, the negative electrode active material may further comprise a treatment, for example, as discussed in FIG. 4. For example, the treatment may be at least one of oxysilane, poly(vinylpryidine), or multivalent metal inorganic salt. In one example, the treatment may be poly(vinylpyridine).

[0089] Turning to FIG. 8, an example method 800 is shown for coating the electrode active material with an inorganic, such as AIPO4, wherein the inorganic AIPO4 is covalently bound to the structures on the surface of the electrode active material. Typically, though not necessarily, the electrode active material to be modified is an electrode active material for a lithium ion battery. Further, when treated, these materials may have a morphology, shape and size appropriate for battery applications. In example method 800, LTO is used to describe the surface layer formation; however, other electrode active materials may be treated using method 800.

[0090] At 802, the method may include receiving the electrode active material structures. In one example, the electrode active material structures may be negative electrode active materials. In another example, the electrode active material structures may be positive electrode active materials. For example, shapes of the electrode active material may include round particles, squared particles, needles, plates, sheets, fibers, hollow tubes, porous particles, dense particles, flakes, spheres, and combinations of any of these. The electrode active material particles may have an average particles size of about ΙΟμηι to about 50μηι, or about Ι μηι to about ΙΟμηι, wherein "about" for the particle size may be taken to mean a d50 particle size. For example, about ΙΟμηι may be read as the d50 particle size is ΙΟμηι.

[0091] For example, negative electrode active material particles ready for use in electrode fabrication may have relatively small average dimensions, e.g., about ΙΟμηι to about 400μηι, and they may sometimes have agglomerates of about Ι μηι to about ΙΟμηι. In another example, certain carbon electrode active material particles ready for use in electrode fabrication may have relatively large dimensions, e.g., about 1 μηι to about 30μηι. The average values present here represent the average largest/principal dimension of the particles. Some types of particles are not substantially spherical (e.g., they are shapes as flakes, rods, ovals, pillows, etc.) and therefore have two or more dimensions. It should also be noted that some materials may have a large variance in particle size, with some particles being substantially larger or smaller than the average dimension presented above.

[0092] For example, the negative electrode active materials include materials capable of intercalating or inserting an alkali metal ion such as lithium or sodium ions. Some of these materials are deployed in commercial lithium ion batteries, while others are under investigation for lithium ion batteries. Examples of negative active material structures that may be surface modified in accordance with the methods disclosed herein include carbons (e.g. graphite, fullerenes, and graphene), silicon, tin, titanium, germanium, the oxides of any of these, the alloys of any of these, and the like. In one example, the negative electrode active materials may comprise lithium titanate. In another example, the negative electrode active materials may comprise a doped lithium titanate.

[0093] In some embodiments, receiving the electrode active material may include performing a preliminary surface treatment, for example as described in regards to FIG. 4.

[0094] At 804, the method may include preparing an inorganic AIPO4 colloidal solution. The inorganic colloidal solution may comprise a solvent, wherein the solvent is water, for example, or the solvent is a non-aqueous compound. In other examples, the method may include providing an AIF₃, AI2O₃ or other similar inorganic colloidal solution. The colloidal solution may be prepared from precursor materials of the inorganic. The inorganic precursors may comprise water soluble salts. In one embodiment, a salt comprising a phosphate anion and a salt comprising an aluminum cation may be used. In some embodiments, one or more water soluble salts may be included. The water soluble salts may be chosen to have a pH that is neutral, pH of 7, or greater than neutral, pH > 7, and thus may not react with LTO, which typically has a pH >9. In this example, the inorganic precursor materials form AIPO4, wherein the inorganic precursor materials are Α1(Ν0₃)3*9¾0 and (NH₄)₂HP0₄. In another example, the inorganic precursor materials may form A1P0₄, wherein the inorganic precursor materials may be A1(C2¾02)3 and K3PO4. The inorganic precursor materials may be combined in an aqueous solution to form the inorganic.

[0095] Further, the method may include an additional additive to enhance further the surface layer formed on structures of the electrode active material for optimization of cell performance. Thus, method 800 may further comprise an additive added to the colloidal solution. A series of experiments have been conducted to determine the effects of surface treatment or, more specifically, effects of forming surface layers covalently bound to electrode active material structures on a performance of electrochemical cells fabricated with these structures.

[0096] LTO was used as a negative active material in these experiments. LTO is believed to catalyze certain reactions that result in gas evolution and an increased resistance of electrochemical cells. Specifically, the presence of hydroxyl groups on the surface of LTO structures is believed to cause electrolyte decomposition and degassing. Elimination or blocking of these hydroxyl groups should help to reduce outgassing and improve other characteristics.

[0097] At 806, the method may include dispersing the electrode active material of 802 into the colloidal solution of 804. The electrode active material may react with the provided inorganic to form a covalently bound surface layer on structures of the electrode active material. In one example, the solvent being present as water may catalyze the formation of the surface layer on the negative electrode active material structures. For example, the resultant mixture may be mixed for a time period. The weight percent of the inorganic, AIPO4, may be chosen to form a monolayer on the surface of the LTO. The monolayer may provide full or partial coverage of the electrode active material particle. For example, the amount of AIPO4 may be added in excess to the calculated weight percent amount to provide a full monolayer which covers the particles uniformly. However, in another example, the amount of AIPO4 may be added insufficient to the calculated weight percent amount to provide a partial monolayer which partially covers the particles. In one example, the weight percent amount of AIPO4 may be less than 2.0 wt. %. In other examples, the weight percent amount of AIPO4 may be less than 1.15 wt. %. In still yet other examples, the weight percent amount of AIPO4 may be less than 1.0 wt. %. However, even partial coverage of the LTO particle may improve the chemical stability and increase the cycle life.

[0098] For example, the amount of AIPO4 available to form a monolayer of Lii+_xAl_xTi2- x(P0₄)3, may be estimated using the ionic radii of the constituent AIPO4 atoms. The monolayer may have a thickness of about 0.75 nm, wherein the monolayer thickness may vary based on the values used for the ionic radii of the coating material. The monolayer thickness may be greater than Onm. In one example, the monolayer thickness may be less than lnm and greater than Onm. The weight ratio of AIPO4 may vary based on the surface area of the electrode active material in order to achieve the monolayer thickness. For example, for a surface area of the electrode active material greater than 5.3 m²/g a weight percentage of AIPO4 may be less than about 2 wt. % and greater than about 1 wt. %. In another example, for a surface area of the electrode active material being between about 2.6 m²/g to about 5.3 m²/g, a weight percentage of AIPO4 may be less than about 1 wt. % and greater than about 0.5 wt. %. In another example, for a surface area of the electrode active material being between about 1.3 m²/g to about 2.6 m²/g, a weight percentage of AIPO4 may be less than about 0.5 wt. % and greater than about 0.25 wt. %. In yet another example, for a surface area of the electrode active material being between about 1.3 m²/g to about 2.6 m²/g, a weight percentage of AIPO4 may be less than about 0.25 wt. % and greater than about 0.15 wt. %. The use of the term about regarding the weight percentage of the AIPO4 includes values within a range which would provide a monolayer of the AIPO4 on the electrode active material.

[0099] At 808, the method may include removing the solvent from the resultant mixture comprising the AIPO4 colloidal solution with the electrode active material dispersed therein to form the electrochemically active material coated with the AIPO4. For example, the resultant mixture may be heated while continuously stirring to evaporate the solvent. In further examples, the resultant mixture may be heated at reduced pressure and/or during gas purging to reduce the concentration of solvent vapor above the resultant mixture and to further stimulate the solvent removal.

[0100] At 810, the method may include drying the resultant powder obtained from removing the solvent at 808. The drying temperature must be sufficient to remove water at a given ambient pressure. For example, the drying may be done in air at 120°C. In another example, drying may be done at temperatures lower than 100°C, when a flow of air is present. In yet another example, drying may be done at temperatures lower than 100°C when the drying is performed under vacuum. In still yet other examples, drying temperatures may be as high as 200°C or 300°C to remove the solvent.

[0101] At 812, the method may include heat treating the dried powder of 810. The heat treating may be done in air at increased temperatures. For example, the heat treating may be done at 500°C to 900°C. In one example, the heat treating may be done at 500°C to 700°C.

[0102] At 814, the method may include obtaining the surface-treated electrode active material. The surface-treated electrode active material may include the presence of hybrid surface structures formed at the surface of the electrode active material particles. For example, a surface layer of AIPO4 formed on structures on the surface of LTO particles may be present, wherein the AIPO4 is covalently bound to the LTO structure. The surface layer on the surface of the electrode active material may have a thickness less than 10 nm, less than 8 nm, or less than 5nm. For example, the surface layer may have an average thickness of about 1 nm. In another example, the thickness of the surface layer on the surface of the electrode active material may be between 0.5 nm to 10 nm.

[0103] At 816, the method further comprises preparing a slurry comprising the surface- treated electrode active material configured for coating onto a current collector. For example, the resultant surface-treated electrode active material may be mixed with a suitable solvent to form a slurry and coated onto a conductive substrate, e.g. a current collector. Further, additional additives and/or binders may be included. In one example, the slurry further comprises a polymer binder selected from the group consisting of polyacrylonitrile, poly(methylmethacrylate), poly (vinyl chloride), polyvinylidene fluoride, poly (vinylidene fluoride-co-hexafluoropropene), polyacrylic acid, styrene butadiene rubber, carboxymethylcellulose and copolymers thereof, the surface-treated electrode active material, coating the slurry onto a current collector. The current collector may be coated on one side or on both sides. In certain embodiments, the slurry may include conductive additives, though in certain cases no conductive additives may be present in the slurry.

[0104] At 818, the method may include fabricating an electrode for use in a battery. For example, the method may include several suboperations such as drying the coated current collector, thereby forming an electrode active material layer on the current collector. The method may further comprise calendaring and slitting the electrodes, assembling the electrodes into a stack or jelly roll, and performing later battery assembly operations. The method may then end.

[0105] FIG. 8 illustrates an example method of forming a surface-treated electrode active material wherein the method includes forming a surface layer on negative electrode active material structures for use in a lithium ion battery. The method comprises receiving a negative electrode active material comprising titanium, preparing a colloidal solution comprising inorganic precursor materials to form AIPO4. The inorganic precursor material including a phosphate salt and an aluminum salt. For example, the inorganic precursor materials phosphate salt is (ΝΗ4)₂ΗΡ0₄ and the aluminum salt is Α1(Ν03)3*9]¾0. The method further comprises mixing the negative electrode active material into the prepared colloidal solution to form a resultant mixture, drying the resultant mixture and then heat treating the dried to obtain a surface-treated electrode active material wherein the surface- treated electrode active material comprises a surface layer of an inorganic AIPO4 covalently bound to the negative electrode active material. The surface-treated electrode active material, for example as described at FIGS. 2 and 3, comprises a surface layer of an inorganic covalently bound to the negative electrode active material structures. The surface layer reduces reactivity of the negative electrode active material structures with respect to the electrolyte. In some examples, the negative electrode active materials may comprise lithium titanate, as discussed above, or another negative electrode active material with similar active material structures. Further, the electrode active material may include other surface treatments, for example, as discussed in regards to FIG. 4.

[0106] Thus, in example method 800 above, a surface-treated electrode active material is provided. The method may further comprise preparing a slurry comprising the surface- treated electrode active material, coating the slurry onto a current collector, and drying the slurry on the current collector, thereby forming an anode. The slurry may further comprise a polymer binder selected from the group consisting of polyacrylonitrile, poly(methylmethacrylate), poly (vinyl chloride), polyvinylidene fluoride, poly (vinylidene fluoride-co-hexafluoropropene), polyacrylic acid, styrene butadiene rubber, carboxymethylcellulose and copolymers thereof. The method may further comprise fabricating a lithium ion battery, further comprising a cathode, a separator, an electrolyte and an anode as described in FIGS. 4A, 4B, 1 1 , 19 and 20, where the AIPO4-LTO phase may convert to a Lii_+xAl_xTi₂-_x(P0₄)3 structure during operation of the battery during a first cycle, i.e. first charge/discharge cycle, as illustrated in reaction 3 above and in FIGS. 2, 3, and 6.

[0107] In one embodiment, a non-aqueous electrolyte battery comprising a cathode and an anode, for example as described above may be provided. The cathode may comprise a positive electrode active material and the anode may comprise a negative electrode active material for intercalating and deintercalating lithium ions comprising titanium and an inorganic A1P0₄ surface layer on at least a portion of a surface of the negative electrode active material. For example, the negative electrode active material may comprise lithium titanate. The ratio of the anode to cathode (anode/cathode) capacity may be less than 1 in order to compensate for the lithium ions lost during the first cycle charge/discharge in forming Lii_+xAl_xTi₂-_x(P0₄)3 structures.

[0108] The non-aqueous electrolyte battery may further comprise a non-aqueous electrolyte comprising at least one salt and at least one solvent. For example, as discussed previously, the electrolyte may comprise L1PF₆ as the electrolyte salt. The non-aqueous electrolyte battery may further comprise a separator, as described previously, positioned between the cathode and the anode.

[0109] The negative electrode active material, as described regarding the methods above, may further comprise an inorganic AIPO4 surface layer, wherein the inorganic AIPO4 surface layer is on at least a portion of a surface of the negative electrode active material, in accordance with some of the embodiments disclosed. The inorganic AIPO4 surface layer may be covalently bound to surface structures of the negative electrode active material. The surface layer forming a Lii_+xAl_xTi₂-_x(P0₄)3 structure during a charge/discharge cycle of the non-aqueous electrolyte battery. For example, Lii_+xAl_xTi₂-_x(P0₄)3 structure may form during cell formation, wherein cell formation occurs during the first charge/discharge cycle. Further, in some embodiments, additional composite surface structures may be present on at least a portion of a surface of the negative titanium electrode. For example, the surface- treated negative electrode active material comprising the inorganic AIPO4 may further comprise AIPO4 and L13PO4 structures on the surface-treated negative electrode active material.

[0110] The non-aqueous electrolyte battery may further comprise an additive to enhance the Lii_+xAl_xTi₂-x(P04)3 structure. For example, the additive may be a tri-alkyl phosphate, as described previously. The tri-alky phosphate additive may be trioctylphosphate.

[0111] Turning to FIG. 9, a SEM 900 of the resultant surface-treated electrode active material is shown, wherein the electrode active material is LTO and the surface layer is AIPO4. Generally, the surface-treated LTO active material particles show a uniform particle size distribution, and remained spherical in shape after coating with the AIPO4, which is covalently bound to the structures on the LTO particle, as described previously at FIGS. 2 and 3. The Al 1000 and P 1002 ion maps corresponding to the SEM image, shown in FIGS. 10A and 10B respectively, show the distribution of the ions appearing uniformly on the surface of the surface-treated LTO active material particles.

[0112] Turning to FIG. 1 1, an example of an electrochemical cell is shown. A brief description of the electrochemical cell is provided for better understanding of some electrolyte features as well as components that come in contact with the electrolyte and expose the electrolyte to certain potentials. In FIG. 1 1, a schematic cross-sectional view of a cylindrical wound cell 1 100, in accordance with some embodiments. Positive electrode 1 106, negative electrode 1 104, and separator strips 1 108 may be wound into a jelly roll, which is inserted into a cylindrical case 1 102. The jelly roll is formed into a shape of case 1 102 and may be cylindrical for cylindrical cells and a flattened oval for prismatic cells. Other types of electrode arrangements include stacked electrodes that may be inserted into a hard case or a flexible case. [0113] The electrolyte, not shown, is supplied into case 1 102 prior to sealing cell 1 100. The electrolyte soaks into positive electrode 1 106, negative electrode 1 104, and separator strip 1 108, all of which are porous components. The electrolyte provides ionic conductivity between positive electrode 1 106 and negative electrode 1 104. As such, the electrolyte is exposed to the operating potentials of both electrodes and comes in contact with essentially all internal components of cell 1 100. The electrolyte should be stable at these operating potentials and should not damage the internal components.

[0114] Case 1 102 may be rigid, for example with lithium ion cells. In other types of cells, the cells may be packed into a flexible, foil-type (polymer laminate) case. For example, pouch cells are typically packed into a flexible case. A variety of materials may be chosen for case 1 102. Selection of these materials depends in part on an electrochemical potential to which case 1 102 is exposed. More specifically, the selection depends on which electrode, if any, case 1 102 is connected to and what the operating potentials are of this electrode.

[0115] If case 1 102 is connected to positive electrode 1106 of a lithium ion battery, then case 1 102 may be formed from titanium 6-4, other titanium alloys, aluminum, aluminum alloys, and 300-series stainless steel. On the other hand, if case 1 102 is connected to negative electrode 1 104 of the lithium ion battery, then case 1 102 may be made from titanium, titanium alloys, copper, nickel, lead, and stainless steels. In some embodiments, case 1 102 is neutral and may be connected to an auxiliary electrode made, for example, from metallic lithium. An electrical connection between case 1 102 and this electrode (e.g., an outer wind of the jelly roll), by a tab connected to the electrode and case 1 102, and other techniques. Case 1 102 may have an integrated bottom as shown in FIG. 1 1. Alternatively, a bottom may be attached to the case by welding, soldering, crimping, and other techniques. The bottom and the case may have the same or different polarities (e.g., when the case is neutral). [0116] The top of case 1 102, which is used for insertion of the jelly roll, may be capped with a header assembly that includes a weld plate 1 1 12, a rupture membrane 11 14, a washer 1 116, header cup 1 1 18 are all made from conductive material and are used for conducting electricity between an electrode (negative electrode 1 104 in FIG. 11) and a cell connector. Insulating gasket 1 1 19 is used to support the conductive components of the header and insulate these components from case 1 102. Weld plate 11 12 may be connected to the electrode by tab 1 109. One end of tab 1 109 may be welded to the electrode (e.g., ultrasonic or resistance welded), while the other end of the tab may be welded to weld plate 1 112. Centers of weld plate 1 112 and rupture membrane 1 1 14 are connected due to the convex shape of rupture membrane 1 114. If the internal pressure of cell 1 100 increases (e.g., due to electrolyte decomposition and other outgassing processes), rupture membrane 1 1 14 may change its shape and disconnect from weld plat 1 1 12, thereby breaking the electrical connection between the electrode and the cell connector.

[0117] PCT washer 1 1 16 is disposed between the edges of rupture membrane 1 1 14 and edges of header cup 1 1 18 effectively interconnecting these two components. At normal operating temperatures, the resistance of PCT washer 1 1 16 is low. However, its resistance increases substantially when PCT washer 1 1 16 is heated up due to, e.g., heat released within cell 1 100. PCT washer 11 16 is effectively a thermal circuit breaker that can electrically disconnect rupture membrane 11 14 from header cup 1 118 and, as a result, disconnect the electrode from the cell connector when the temperature of PCT washer 1 116 exceeds a certain threshold temperature. In some embodiments, a cell or battery pack may use a negative thermal coefficient (NTC) safety device in addition to or instead of a PCT device.

[0118] Also provided herein are battery packs, each containing one or more electrochemical cells built with processed active materials. When a battery pack includes multiple cells, these cells may be configured in series, in parallel, or in various combinations of these two connection schemes. In addition to cells and interconnects (electrical leads), battery packs may include charge/discharge control systems, temperature sensors, current balancing systems, and other like components. For example, battery regulators may be used to keep the peak voltage of each individual cell below its maximum value so as to allow weaker batteries to be fully charged, thereby bringing the whole pack back into balance. Active balancing can also be performed by battery balancer devices that can shuttle energy from stronger batteries to weaker ones in real time for improved balance.

[0119] In certain embodiments, a positive electrode includes one or more active materials and a current collecting substrate. The positive electrode may have an upper charging voltage of about 3.5-4.5 volts versus a Li/Li⁺ reference electrode. The upper charging voltage is the maximum voltage to which the positive electrode may be charged at a low rate of charge and with significant reversible storage capacity. In some embodiments, cells utilizing a positive electrode with upper charging voltages from about 3-5.8 volts versus a Li/Li⁺ reference electrode are also suitable. In certain instances, the upper charging voltages are from about 3-4.2 volts, about 4.0-5.8 volts, or about 4.5-5.8 volts. In certain instances, the positive electrode has an upper charging voltage of about 5 volts. For example, the cell can have an upper charging voltage of about 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7 or 5.8 volts. A variety of positive electrode active materials can be used. Non-limiting illustrative electrode active materials include transition metal oxides, phosphates and sulfates, and lithiated transition metal oxides, phosphates and sulfates.

[0120] In some examples, the suitable positive electrode-active compounds may be further modified by doping with about 5% or less of divalent or trivalent metallic cations such as Fe²⁺, Ti²⁺, Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺, Mg²⁺, Cr³⁺, Fe³⁺, Al³⁺, Ni³⁺ Co³⁺, or Mn³⁺, and the like. In other embodiments, positive electrode active materials suitable for the positive electrode composition include lithium insertion compounds with olivine structure such as Li_xMX0_4; where M is a transition metal selected from Fe, Mn, Co, Ni, and a combination thereof, X is a selected from P, V, S, Si and combinations thereof, and the value of the value x is between about 0 and 2. In certain instances, the compound is L1MXO4. In some embodiments, the lithium insertion compounds include LiMnP04, L1VPO4, L1C0PO4 and the like. In other embodiments, the active materials have NASICON structures such as Y_XM2(X0₄)3, where Y is Li or Na, or a combination thereof, M is a transition metal ion selected from Fe, V, Nb, Ti, Co, Ni, Al, or the combinations thereof, X is selected from P, S, Si, and combinations thereof, and the value of x is between 0 and 3. Particle size of the electrode materials may be between about 1 nm and about 100 μηι, between about 10 nm and about 100 μηι, or between about 1 μηι and 100 μηι.

[0121] In other embodiments, the electrode active materials are oxides such as L1C0O2, spinel LiMn₂0₄, chromium-doped spinel lithium manganese oxides Li_xCr_yMn₂0₄, layered LiMn₂0₄, LiNiC , or LiNi_xCoi__x0₂, where x is between about 0 and 1, or between about 0.5 and about 0.95. The electrode active materials may also be vanadium oxides such as L1V2O₅, L1V6O13, or the foregoing compounds modified in that the compositions thereof are nonstoichiometric, disordered, amorphous, overlithiated or underlithiated.

[0122] In yet other embodiments, positive electrode active materials suitable for the positive electrode composition include lithium insertion compounds with olivine structure such as LiFeP0₄ and with NASICON structures such as LiFeTi(S0₄)3. In still other embodiments, electrode active materials include LiFePC^, LiMnPC^, L1VPO4, LiFeTi(S04)3, LiNi_xMni__x02, LiNi_xCo_yMni-_x-_y02 and derivatives thereof, wherein x and y are each between about 0 and 1. In certain instances, x is between about 0.25 and 0.9. In one instance, x is 1/3 and y is 1/3. Particle size of the positive electrode active material should range from about 1 to 100 microns. [0123] In some embodiments, the electrode-active material includes transition metal oxides such as L1C0O2, LiMn20₄, LiNiC , LiNi_xMni__x02, LiNi_xCo_yMni__x__y02 and their derivatives, where x and y are each between about 0 and 1. LiNi_xMni__x02 can be prepared by heating a stoichiometric mixture of electrolytic MnC , LiOH and nickel oxide to between about 300°C and 400°C. In certain embodiments, the electrode active materials are xLi₂Mn03(l-x)LiM0₂ or LiM'P0₄, where M is selected Ni, Co, Mn, LiNi0₂ or LiNi_xCoi__x0₂; M' is selected from Fe, Ni, Mn and V; and x and y are each independently a real number between about 0 and 1. LiNi_xCo_yMni-_x-_y02 can be prepared by heating a stoichiometric mixture of electrolytic MnC , LiOH, nickel oxide and cobalt oxide to between about 300°C and 500°C. The positive electrode may contain conductive additives from 0% to about 90%. In one embodiment, the subscripts x and y are each independently selected from 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.95, and x and y can be any numbers between 0 and 1 to satisfy the charge balance of the compounds LiNi_xMni__x0₂ and LiNi_xCo_yMni__x__y0₂.

[0124] Regarding FIGS. 12 through 18, the prepared surface-treated electrode active material, for example as outlined in method 800 in FIG. 8, may be used for making an electrode which is coated on both sides. The surface-treated electrode active material may comprise an inorganic-AlP0₄ surface layer in direct contact with a lithium titanate electrode active material. The electrode may then be used to make stack plates in 2.2 Ah pouch cells. The cathode may be a standard matching lithium manganese oxide (LMO) electrode. Control cells were made for comparison wherein the LTO had no A1P0₄ coating (uncoated LTO), the LTO had an A1₂0₃ coating (Al₂0₃-LTO), and the LTO had a carbon coating (C-LTO). The properties of the cells were measured as described below. The cells were assembled with a lithium manganese oxide (LMO) cathode and an LTO anode. [0125] For example, the control cell with uncoated LTO may be prepared using LTO powder as received to fabricate an electrode with no surface treatments.

[0126] For example, the control cell with the AI2O3-LTO coating may be prepared via traditional AI2O3 coating processes. In one example, the LTO powder may be added into an A1(N0₃)3 solution with continuous stirring for 1 hour, and then Νί¾*Η₂θ was slowly added into the solution and the pH was controlled to be about 8. This mixture is kept at 80°C for 5 hours until most of the solvent has evaporated. The powder is then dried at 120°C for 12 hours and then sintered at 500°C for 6 hours to produce the AI2O3-LTO powder for use in fabricating an electrode for a Li-ion cell. In another example, the LTO powder may soaked in 10 mmol dm^"3 2-propanol containing aluminum tri 2-proposide (99% Soekawa chemicals) for 3 hours and then filtered. The LTO whose surface is modified by aluminum oxide was then obtained through heat treatment at 400°C for 4 hours to produce the AI2O₃-LTO powder for use in fabrication an electrode for a Li- ion cell.

[0127] The cells comprising AIPO4 surface-treated LTO active material showed higher starting impedance than the control cells, uncoated LTO and AI2O3 LTO, during a beginning of life (BOL) test at 30 % state of charge (SOC) at 1 kHz. For example, the cells comprising AIPO4 surface-treated LTO active material (AIPO4-LTO cell) had a 30% SOC BOL impedance of 2.16 mOhm as compared to the control cell at 1.58 mOhm. The first cycle coulombic efficiency for the cells, provided in table 2 below, was lower for the AIPO4-LTO cell than for the control cells with the uncoated LTO, AI2O3-LTO and C-LTO. This indicates that the reaction to form Lil+_xAl_xTi2-_x(P04)3 structure took place, consuming some lithium. In some embodiments, in order to compensate for this loss of lithium, a cathode capacity may exceed an anode capacity. The ratio of the capacity of the anode to the capacity of the cathode per matching surface area is often referred to as the A/C ratio. In one example, the A/C ratio for the cells including the surface-treated electrode active material comprising AIPO4 coating, AIPO4-LTO, may be less than 1. In other examples, the A/C/ ratio may be less than 0.9, less than 0.8, less than 0.7 or less than 0.6. In yet other examples, the A/C ratio may be between 0.7 and 0.9. The A/C ratio being between 0.7 and 0.9 is preferred as it provides for higher energy density and good cycle life.

TABLE 2: First Cycle Efficiency for Li-ion cells

[0128] Turning to FIG. 12, the capacity retention 1200 of a Li-ion cell at 50°C including a surface-treated electrode active material is illustrated, in accordance with some embodiments. The AIPO4-LTO cell is illustrated at curve 1202 and the control cell with uncoated LTO is illustrated at curve 1204. The AIPO4-LTO cell shows significant improvement in cycle life as compared to the control cells over 300 cycles at 50°C.

[0129] Turning to FIG. 13, the capacity retention 1300 of a Li-ion cell at 60°C including a surface-treated electrode active material, in accordance with some embodiments is shown. The AIPO4-LTO cell is illustrated at curve 1302 and the control cell with uncoated LTO is illustrated at curve 1304. The AIPO4-LTO cell shows significant improvement in cycle life as compared to the control cells over 300 cycles at 60°C.

[0130] Turning to FIG. 14, the capacity retention 1400 of a Li-ion cell over a temperature range including a surface-treated electrode active material, in accordance with some embodiments is shown. The AIPO4-LTO cell is illustrated at 50°C, 65°C, and 75°C at 1402, 1404, and 1406 respectively. Thus, the AIPO4-LTO cell shows improved capacity retention at increased temperatures over many cycles as compared to the control cells. [0131] The performance observations of the inorganic AIPO4 LTO noted above in the BOL and the capacity retention at 50°C and 60°C are believed to be due to the surface-treated electrode active material having hybrid AIPO4-LTO surface structures, which form at the surface of the LTO and extend into the electrolyte phase, during a first charge/discharge cycle. When a surface coating consisting of AIPO4 (for example prepared from a colloidal precipitate of A1(N0₃)3 and (NH4)2HP0₄) is applied to the LTO surface followed by heat treatment, for example as described in FIG. 3, a hybrid AIPO4-LTO phase is formed at the surface. Without being restricted to any particular theory, it is believed that the hybrid structure is similar to the Lii+_xAl_xTi2-_x(P04)3 structure. The Lii+_xAl_xTi2-_x(P04)3 structure is electronically insulating but has a high relative lithium room temperature ion conductivity and is known to be a good solid state ionic conductor. Further, it is also believed that the AIPO4-LTO phase converts fully to the Lii_+xAl_xTi2-_x(P04)3 structure occurs during the first cycle. The formation of Lii_+xAl_xTi2-_x(P04)3 from AIPO4 and LTO is facilitated by the charge/discharge redox conditions, in addition to the heat treatment, in the first cycle and results in the consumption of lithium ions and electrons thus resulting in the lower first cycle efficiency value as discussed above. The low first cycle efficiency, and associated reactions, may be necessary to create a robust LTO-electrolyte interface and yield the observed cycle life enhancement. The resultant Lii_+xAl_xTi2-_x(P04)3 structure formed through combination of heat treatment and reduction may reduce the catalytic activity of the Ti (III) - O site on the LTO surface. This may reduce the number of degradation reactions that may occur with the electrolyte, for example as described in FIG. 1, thereby minimizing solid degradation products, stabilizing the LTO-electrolyte interfacial impedance, and promoting improved cycle life. Additionally, Lii_+xAl_xTi2-_x(P04)3 allows high Li⁺ transport during charge (Li⁺ insertion) and discharge (Li⁺ de-insertion) in the LTO spinel structure. [0132] The surface layer on the surface-treated electrode active material is believed to mitigate electrolyte degradation reactions and/or inhibit surface LTO phase changes that may result in increases in charge transfer resistance. A coating which partially covers the LTO surface with a monolayer may provide protection and may further improve battery properties, such as improved discharge and regeneration power.

[0133] Turning to FIGS. 15 and 16, a discharge 1500 and a regeneration 1600 hybrid pulse power characterization (HPPC) test, respectively, before and after 24 hour soak, storage, at 66°C are illustrated for a 1 second pulse power at 50% SOC. The cells comprised the AIPO4-LTO electrodes. In FIG. 15, the AIPO4-LTO cell before storage 1502 and after 24 hour soak 1504 show a discharge HPPC at or below 5% 1506. In FIG. 16, the AIPO4-LTO cell before storage 1602 and after 24 hour soak 1604 show a regeneration at or below 5%. The results show that the discharge and regeneration power degradation was at or below 5% and thus satisfied the automotive battery requirements.

[0134] Turning to FIG. 17, the power at 100% SOC during cold cranking at -30°C of a Li-ion cell including a surface-treated electrode active material, in accordance with some embodiments is illustrated. The AIPO4-LTO cell 1702 and the control cell 1704 show no significant difference from one another. Thus, the AIPO4 surface treatment of the LTO electrode active material in the AIPO4-LTO cell does not limit the performance of the Li-ion battery during cold cranking or, in general, at low temperatures.

[0135] Turning to FIG. 18, a useable Energy Determination of a Li-ion cell including a surface-treated electrode active material, in accordance with some embodiments is illustrated. The control cell discharge 1802 and regeneration 1806 at 10 seconds is compared to the AIPO4-LTO cell discharge 1804 and regeneration 1808. The discharge and regeneration power is seen to be different for the control cell and AIPO4-LTO cell. Both the discharge and regeneration power are lower for the AIPO4XTO cell. [0136] The performance observations for the surface-treated electrode active material disclosed herein may be rationalized by the presence of hybrid AIPO4-LTO surface structures formed at the interface of the bulk LTO and extending into the electrolyte phase. For example, when a surface coating comprising AIPO4, prepared as described above as a colloidal solution, is mixed with LTO and that is followed by heat treatment between 500°C and 900°C, a hybrid AIPO4-LTO phase is formed at the surface of the LTO particles. The structure at this interface is thought to be similar to the Lii_+xAl_xTi2-_x(P04)3 structure. Beyond the interface and if sufficient AIPO4 is present, AIPO4 is likely to exist. The Lii_+xAl_xTi2- _Χ(Ρ04)3 structure is electronically insulating but has a high ionic conductivity. Further, it is believed that the additional conversion of the AIPO4-LTO surface structures to the AIPO4- LTO hybrid phase comprising Lii_+xAl_xTi2-_x(P04)3 occurs during the first cycle, e.g., cell formation. The formation of the Lii_+xAl_xTi2-_x(P04)3 from AIPO4 and LTO is facilitated by the charge/discharge redox conditions, in addition to the heat treatment, in the first cycle and results in the consumption of lithium, thus resulting in the lower first cycle efficiency value, as described above. The low first cycle efficiency, and associated reactions, may be necessary to create a robust LTO-electrolyte interface and yield the observed increase in cycle life and survivability at high temperatures in Li-ion cells.

[0137] In some embodiments, the capacity of the cathode is larger than the capacity of the anode. The anode to cathode capacity, also referred to as an A/C ratio or anode/cathode ratio, for typical Li-ion cells is greater than 1. However, in this case, as Li ions are lost during the first cycle to the anode as described above, the A/C ratio may be less than 1. In one example, the A/C ratio may be less than 0.9. In another example, the A/C ratio may be less than 0.8. In yet another example, the A/C ratio may be between 0.7-0.9. For example, setting the A/C ratio to be less than 1 , excess Li ions may be available in the cell to form the LTO-electrolyte interface. [0138] In some embodiments, the LTO potential may be pushed to a lower voltage to saturate the structures with Li and on the first charge, cell formation, the cell may be charged to above the recommended voltage of 2.7V when paired with such cathode materials as LMO, NCM and LCO. For example, the cell may be charged up to 2.9V, or 3.0V, or 3.2V, or 3.4V. In other example, the cell may be charged up to 4.3V. Under these charging conditions, the LTO potential may reach 1.4V, 1.3V, 1.2V, or as low as 0.2V versus a standard Lithium electrode potential. Additional exposure of a charged cell to higher temperature may further facilitate creation of robust structures on the LTO surface. The heat exposure can be to 60-85°C for a period of time of 1 hour to 7 days. The length and the temperature of the exposure may be chosen based on the temperature the batteries are exposed to in real application, for example, the temperature of the exposure should be higher than the maximum temperature that application requires. In one example regarding automotive applications, temperatures of 50°C or 65°C or 85°C may be experienced by a cell, depending on the location of the battery and the climate in specific geographical area.

[0139] Further, without wishing to be bound to a theory, it is also thought that the Lii_+xAl_xTi₂-x(P0₄)3 interfacial layer formed through the combination of heat treatment and reduction reduces the catalytic activity of the Ti(III)-0 site on the lithium titanate surface. The reduction in catalytic activity may reduce the number of degradation reactions that occur with the electrolyte, thereby minimizing solid degradation products, stabilizing the LTO- electrolyte interfacial impedance, and promoting improved cycle life. Additionally, as discussed above, Lii+_xAl_xTi2-_x(P04)3 in a known lithium ion conductor allowing a high Li⁺ transport during charge (e.g., Li⁺ insertion) and during discharge (e.g., Li⁺ de-insertion) in the LTO structure.

[0140] The embodiments described may be used in prismatic and cylindrical electrochemical cells. For purposes of this document, a prismatic cell is defined as a cell having a rectangular profile within a plane perpendicular to the length of the cell. In other words, the prismatic cell has a rectangular profile within a plane formed by its thickness and width. Prismatic cells should be distinguished from round (cylindrical) cells that have a circular profile within this plane.

[0141] Prismatic cells may generally conform better to battery cases and other enclosures, as compared to round cells. This may be especially true where multiple cells are packed side by side in the enclosure. Further, in a stack design, prismatic cells tend to have better current delivery capabilities, as there are multiple cathodes and multiple anodes and corresponding tabs forming such cells. Round cells typically have a single cathode, single anode, and one or more tabs attached to each electrode. As such, prismatic cells may be made into larger formats and have larger capacities. In certain embodiments, an electrochemical cell including a venting device has a capacity of at least about 1.0 Ah or a capacity of at least about 5 Ah.

[0142] Large capacity electrochemical cells (e.g., cells having a capacity of about 3 Ah or greater) should have more effective safety devices relative to their low capacity counterparts, as there are a lot more safety concerns with the large cells. For example, large cells can cause a lot more damage when they reach a critical pressure level at which the case may burst or some other negative phenomena may occur.

[0143] A rechargeable electrochemical cell includes one or more pairs of positive and negative electrodes, separator, electrolyte providing ionic communication between the electrodes, and an enclosure assembly containing the electrodes and electrolyte. The enclosure assembly may include multiple components that provide mechanical enclosure and electrical communication functions.

[0144] Turing to FIGS. 19A and 19B, a schematic top and side view of a prismatic electrochemical cell 1900 are illustrated respectively, in accordance with certain embodiments. Electrochemical cell 1900 includes an enclosure assembly 1902 that surrounds and encloses an electrode assembly 1920. Enclosure assembly 1902 is shown to include a case 1902a and header 1902b attached to case 1902a. Enclosure assembly 1902 may include other components, such as a case bottom, various seals and insulating gaskets, which are not specifically shown in FIGS. 19A and 19B.

[0145] Header 1902b is shown to include feed- through 1904a and 1904b and venting device 1908. One of these components may be used as a fill plug. Feed-through 1904a and 1904b include corresponding conductive elements 1906a and 1906b that provide electronic communication to respective electrodes in electrode assembly 1920 as further described with reference to FIG. 19C. In certain embodiments, external components of conductive elements 1906a and 1906b may be used as cell terminals for making electrical connections to the battery. Conductive elements 1906a and 1906b may be insulated from header 1902b. In other embodiments, header 1902b and/or 1902a may provide one or both electronic paths to the electrodes in electrode assembly 1920. In some embodiments, a cell may have only one feed-through or no feed-through at all.

[0146] In certain embodiments (not shown), the feed-through and/or venting device may be supported by other components of enclosure assembly 1902, such as the case and/or bottom. Further, the feed-through and/or venting device may be integrated into a header or other components of the enclosure assembly during fabrication of these components or during assembly of the cell. The latter case allows more flexibility in design and production.

[0147] Components of enclosure assembly 1902 may be made from electrically insulating materials, such as various polymers and plastics. These materials need to be mechanically/chemically/electrochemically stable at the specific operating conditions of the cell, including but not limited to electrolytes, operating temperature ranges, and internal pressure build-ups. Some examples of such materials include polyamine, polyethylene, polypropylene, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, and polyethylene terephthalate. Other polymers and copolymers may be used as well. In certain embodiments, components of enclosure assembly 1902 may be made from conductive materials. In these embodiments, one or more components may be used to provide electronic communication to the electrodes. When multiple conductive components are used for enclosure assembly 1902, these conductive components may be insulated with respect to each other using insulating gaskets.

[0148] Conductive elements 1906a and 1906b may be made of various conductive materials such as any metal of metallic alloy. These conductive materials may be isolated from any contact with electrolyte (e.g., external components or components having protective sheaths) and/or electrochemically stable at operating potentials if exposed to electrolyte. Some examples of conductive materials include steel, nickel, aluminum, nickel, copper, lead, zinc and their alloys.

[0149] When enclosure assembly 1902 includes multiple components, such as case 1902a and header 1902b, these components may be sealed with respect to each other. The sealing process used depends on the materials used for the components, and may involve heat sealing, adhesive application (e.g., epoxies), and/or welding (e.g., laser welding, ultrasonic welding, etc.). This sealing is performed after inserting electrode assembly 1920 into enclosure assembly 1902 and typically prior to filling electrolyte into enclosure assembly 1902. Enclosure assembly 1902 may be then sealed by installing venting device 1908 or some other means. However, in certain embodiments the sealing may occur before electrolyte is introduced into the enclosure assembly 1902. In such embodiments, the enclosure assembly should provide a mechanism for filling electrolyte after such sealing has taken place. In one example, the enclosure assembly 1902 includes a filling hole and plug (not shown). [0150] Electrode assembly 1920 includes at least one cathode and one anode. These two types of electrodes are typically arranged such that they face one another and extend alongside one another within the enclosure assembly 1902. A separator may be provided between two adjacent electrodes to provide electric insulation while also allowing ionic mobility between the two electrodes through pores in the separator. The ionic mobility is provided by electrolyte that soaks the electrodes and separator.

[0151] The electrodes are typically much thinner than the internal spacing of enclosure assembly 1902. In order to fill this space, electrodes may be arranged into stack and/or jelly rolls. In a jelly roll, one cathode and one anode are wounds around the same axis (in the case of round cells) or around an elongated shape (in the case of prismatic cells). Each electrode has one or more current collecting tabs extending from that electrode to one of conductive elements 1906a and 1906b of feed-through 1904a and 1904b, or to some other conductive component or components for transmitting an electrical current to the electrical terminals of the cell.

[0152] In a stackable cell configuration, multiple cathodes and anodes may be arranged as parallel alternating layer. One example of a stackable electrode assembly 1920 is shown in FIG. 19C. Electrode assembly 1920 is shown to include seven cathodes 1922a- 1922g and six anodes 1924a-1924f. Adjacent cathodes and anodes are separated by separator sheets 1926 to electrically insulate the adjacent electrodes while providing ionic communication between these electrodes. Each electrode may include a conductive substrate (e.g., metal foil) and one or two active material layers, for example, the surface-treated electrode active material described above, supported by the conductive substrate. Each negative active material layer is paired with one positive active material layer. In the example presented in FIG. 17C, outer cathodes 1922a and 1922g include only one positive active material facing towards the center of assembly 1920. All other cathodes and anodes have two active material layers. One having ordinary skill in the art would understand that any number of electrodes and pairing of electrodes may be used. Conductive tabs may be used to provide electronic communication between electrodes and conductive elements, for example. In certain embodiments, each electrode in electrode assembly 1920 has its own tab. Specifically, electrodes 1922a-1922g are shown to have positive tabs 1910 while anodes 1924a- 1924f are shown to have negative tabs 1908.

[0153] FIGS. 20A and 20B illustrate a schematic top and side view of a wound electrochemical cell example 2000, in which two electrodes are wound into a jelly roll, in accordance with certain embodiments.

[0154] As described above, a method is provided for forming a surface layer on negative electrode active material structures for use in a lithium ion battery. In one example, the negative electrode active material is lithium titanate. The method may comprise receiving a negative electrode active material having structures. Further, a colloidal solution comprising inorganic precursor materials, for example inorganic AIPO4 precursor materials, may be prepared. The inorganic precursor materials may comprise an aluminum salt and a phosphate salt. For example, the inorganic AIPO4 inorganic precursors may be A1(N03)3*9H20 and (NH4)₂HP0₄. The negative electrode active materials may be mixed into the prepared colloidal solution to form a resultant mixture. The resultant mixture may then be dried to remove solvent. The solvent may be water or a non-aqueous solvent. The dried resultant mixture may then be heat treated to obtain the surface-treated electrode active material as described. The surface-treated electrode active material comprises a surface layer of an inorganic which reduces reactivity of the negative electrode active material structures with respect to the electrolyte.

[0155] The surface-treated electrode active material may be used to fabricate an anode for use in a lithium ion cell. A slurry may be prepared comprising the surface-treated electrode active material wherein the slurry is configured for coating onto a current collector. Additional steps such as drying the slurry on the coated current collector may be performed to fabricate the anode. The anode may then be used in a lithium ion battery, wherein the lithium ion battery further comprises a cathode, a separator, and an electrolyte. As discussed above, the surface layer may be fully formed upon operating the lithium ion battery for a first cycle, wherein the AIPO4-LTO phase converts to a Lil_+xAl_xTi₂-_x(P0₄)3 structure.

[0156] In another example, a method is provided for forming a surface layer on negative electrode active material structures for use in a lithium ion battery wherein an additive is included which forms an enhanced surface layer in addition to the surface layer formed from the inorganic. The method may comprise a tri-alkyl phosphate additive wherein the additive enhances the surface layer and covalently bonds to the negative electrode active material structures to form the enhanced surface layer.

[0157] Various modifications of the present invention, in addition to those shown and described herein, will be apparent to those skilled in the art of the above description. Such modifications are also intended to fall within the scope of the appended claims.

[0158] It is appreciated that all reagents are obtainable by sources known in the art unless otherwise specified.

[0159] Patents, publications, and applications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains. These patents, publications, and applications are incorporated herein by reference to the same extent as if each individual patent, publication, or application was specifically and individually incorporated herein by reference.

[0160] The foregoing description is illustrative of particular embodiments of the invention, but is not meant to be a limitation upon the practice thereof. [0161] The foregoing discussion should be understood as illustrative and should not be considered limiting in any sense. While the inventions have been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the inventions as defined by the claims.

[0162] The corresponding structures, materials, acts and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material or acts for performing the functions in combination with other claimed elements as specifically claimed.

[0163] Finally, it will be understood that the articles, systems, and methods described hereinabove are embodiments of this disclosure— non-limiting examples for which numerous variations and extensions are contemplated as well. Accordingly, this disclosure includes all novel and non-obvious combinations and sub-combinations of the articles, systems, and methods disclosed herein, as well as any and all equivalents thereof.

Claims

1. A non-aqueous electrolyte battery, comprising:

a cathode;

an anode comprising a negative electrode active material for intercalating and deintercalating lithium ions comprising titanium and an inorganic AIPO4 surface layer on at least a portion of a surface of the negative electrode active material;

the surface layer forming a Lii_+xAl_xTi2-_x(P0₄)3 structure during a charge/discharge cycle of the non-aqueous electrolyte battery;

a non-aqueous electrolyte being in ionically conductive contact with the anode and the cathode, the electrolyte comprising at least one salt and at least one solvent; and

a separator positioned between the cathode and the anode.

2. The non-aqueous electrolyte battery of claim 1, wherein the negative electrode active material is lithium titanate.

3. The non-aqueous electrolyte battery of claim 1, wherein the inorganic AIPO4 surface layer is covalently bound to the negative electrode active material.

4. The non-aqueous electrolyte battery of claim 1, further comprising AIPO4 and L13PO4 structures as part of the surface layer of the negative electrode active material.

5. The non-aqueous electrolyte battery of claim 1, wherein the non-aqueous electrolyte further comprises an additive to enhance the Lii_+xAl_xTi2-_x(P0₄)3 structure.

6. The non-aqueous electrolyte battery of claim 5, wherein the additive is a tri-alkyl phosphate.

7. The non-aqueous electrolyte battery of claim 6, wherein the additive is trioctylphosphate.

8. The non-aqueous electrolyte battery of claim 1, wherein a ratio of the anode to cathode capacity is less than 1.

9. A surface-treated electrode active material for use in a lithium ion battery, comprising:

a negative electrode active material for intercalating and deintercalating lithium ions comprising titanium; and

an inorganic AIPO4 surface layer wherein the inorganic AIPO4 surface layer is directly adjacent to the negative electrode active material.

10. The surface-treated electrode active material of claim 9, wherein the negative electrode active material is lithium titanate.

1 1. The surface-treated electrode active material of claim 9, wherein the inorganic AIPO4 surface layer is covalently bound to the negative electrode active material.

12. The surface-treated electrode active material of claim 9, wherein the inorganic AIPO4 surface layer is less than 10 nm.

13. The surface-treated electrode active material of claim 9, wherein the surface-treated electrode active material is used in a lithium ion battery.

14. The surface-treated electrode active material of claim 9, wherein the negative electrode active material further comprises a treatment, wherein the treatment is at least one of oxysilane, poly(vinylpyridine), or multivalent metal salt.

15. The surface-treated electrode active material of claim 14, wherein the treatment is poly(vinylpyridine) .

16. A method of forming a surface-treated electrode active material, comprising:

receiving a negative electrode active material comprising titanium;

preparing a colloidal solution comprising inorganic precursor materials to form AIPO4, the inorganic precursor materials including a phosphate salt and an aluminum salt; mixing the negative electrode active material into the prepared colloidal solution to form a resultant mixture; and drying the resultant mixture and then heat treating to obtain a surface-treated electrode active material wherein the surface-treated electrode active material comprises a surface layer of an inorganic AIPO4 covalently bound to the negative electrode active material structures.

17. The method of claim 16, wherein the negative electrode active material comprise lithium titanate.

18. The method of claim 16, wherein the inorganic precursor materials phosphate salt is (NH₄)₂HP0₄ and the aluminum salt is Α1(Ν0₃)₃*9Η₂0.

19. The method of claim 16, further comprising:

preparing a slurry comprising the surface-treated electrode active material wherein the slurry further comprises a polymer binder selected from the group consisting of polyacrylonitrile, polymethylmethacrylate), poly (vinyl chloride), polyvinylidene fluoride, poly (vinylidene fluoride-co-hexafluoropropene), polyacrylic acid, styrene butadiene rubber, carboxymethylcellulose and copolymers thereof;

coating the slurry onto a current collector; and

drying the slurry on the current collector, thereby forming an anode.

20. The method of claim 19, wherein the slurry further comprises a treatment for the surface-treated electrode active material, wherein the treatment is poly(vinylpyridine).

21. The method of claim 19, further comprising:

fabricating a lithium ion battery, further comprising:

a cathode;

an anode;

a separator positioned between the anode and the cathode; and an electrolyte being in ionically conductive contact with the anode and the cathode, the electrolyte comprising at least one salt and at least one non-aqueous solvent; where AIPO4-LTO phase converts to a Lii_+xAl_xTi2-_x(P0₄)3 structure during operation of the battery during a first cycle.

22. The method of claim 21, wherein further adding an additive to the electrolyte to enhance the formation of the Lii+_xAlxTi2-_x(P04)3 structure during the first cycle.

23. The method of claim 22, wherein the additive is a tri-alkyl phosphate.