Electrochemical lithium ion or lithium sulfur secondary cells or batteries comprising silicon-based alloys with multiple separated phases as negative electrode material

Abstract

An electrochemical lithium-ion or lithium-sulfur secondary cell or battery comprising a negative electrode composition utilizing lithium; wherein the lithium is drawn into the negative electrode composition during charging of the cell or battery and is withdrawn from the negative electrode composition during discharging of the cell or battery; the negative electrode material comprising a composite material consisting of silicon, tin, and a second metallic element selected from the group consisting of aluminum, copper, and titanium, wherein the composite material is further characterized in that the silicon, tin, and the second metal are present separately in different phases, the tin phase and the phase of the second metallic element being crystalline or amorphous, and the silicon phase being amorphous;wherein the composite material of silicon, tin and the second metal element is further characterized by nanoscale islands of amorphous silicon phase dispersed in a matrix of a tin phase and a phase of the second metal element, wherein the composite material consists of 50 atomic% silicon, 25 atomic% tin and 25 atomic% of the second metal.

Description

This application is a partial continuation of serial number 13 / 234209, filed on September 16, 2011, entitled “Phase-separated silicon-tin composite material as a negative electrode material for lithium-ion batteries”, now US patent application publication US 2013 / 0071736A1. TECHNICAL AREA This invention relates to the production of negative electrode materials suitable for batteries using lithium electrodes, for example, lithium-ion batteries and lithium-sulfur batteries. More specifically, this invention relates to the production and use of composite material compositions containing nanometer-scale islands of amorphous silicon phases embedded in separate nanometer-scale crystalline or amorphous phases of tin and other metals, for example, aluminum, copper, or titanium. Such composite material compositions can be produced as particles by a rapid solidification process and used as negative electrode materials for the cyclic insertion and extraction of lithium in the operation of lithium batteries.The combination of suitable atomic ratios of silicon, tin and at least one other metallic element and the sizes of the corresponding phases in such composite materials enables the insertion or incorporation of increased amounts of lithium via repeated electrochemical cycles with minimal damage to the particulate negative electrode material. BACKGROUND OF THE INVENTION Lithium-ion batteries are used as electrical storage systems for powering electric and hybrid-electric vehicles. These batteries comprise a number of appropriately interconnected electrochemical cells arranged to deliver a predetermined electric current at a specified electrical potential. In each such cell, lithium, as lithium ions, is transported from a negative electrode through a non-aqueous, lithium-containing electrolyte solution to a lithium-ion accepting positive electrode when an electric current is delivered from the battery to an external load device, such as an electric drive motor. A suitable porous separator material, infiltrated with the electrolyte solution and permeable to the transport of lithium ions in the electrolyte, is used to prevent a physical short circuit between the electrodes.Graphite was used as the negative electrode material and bonded in a thin electrode layer to a copper current collector. During charging, lithium is inserted into the graphite (lithiation, forming LiCl₆, approximately 372 mAh / g), and during discharging, lithium is extracted from the graphitic carbon (delithiation). A suitable particulate material for absorbing and storing inserted lithium during each cell's discharge is used as the positive electrode material. Examples of such positive electrode materials include lithium cobalt oxide (LiCoO₂), a spinel lithium transition metal oxide, for example, spinel lithium manganese oxide (LiMn₂O₅), a lithium polyanion, for example, nickel manganese cobalt oxide [Li(N₂O₅)₅], lithium iron phosphate (LiFePO₄), lithium fluorophosphate (Li₂FePO₄F), or a mixture of any of these materials.Suitable positive electrode materials are often bonded as a thin film to an aluminum current collector. The electrochemical potential of such lithium-ion cells is typically in the range of about 2 to 4.5 volts. The use of lithium-ion batteries to power electric motors in motor vehicles has led to a need for batteries with higher gravimetric and / or volumetric capacity. While graphitic carbon is durable and a useful lithium-intercalating negative electrode material for lithium-ion cells, it has a relatively low capacity for such lithium insertion. Other potential negative electrode materials, for example, silicon (theoretical capacity, 3600 mAh / g, for Li15Si4) and tin (theoretical capacity, 992 mAh / g, for Li22Sn5), have much higher theoretical capacities for lithium insertion than graphite. However, the volume change of up to 300 vol% for silicon during lithiation and delthiation processes leads to fracture of the active silicon material and / or a loss of electrical contact with the conductive additives or current collectors.Tin has the same problem of large volume expansion during lithiation, leading to rapid capacity degradation. Such and similar negative electrodes, as well as lithium secondary cells or batteries, are described, for example, in US 2009 / 0061322A1, US 2010 / 0119942A1, US 2007 / 0020521A1, US 2002 / 0162606A1, and US 2005 / 0130043A1. Lithium-sulfur batteries, like lithium-ion batteries, are rechargeable. They are therefore notable for their high energy density. The low atomic weight of lithium and the moderate atomic weight of sulfur allow lithium-sulfur batteries to be relatively lightweight. Like lithium-ion cells, the anode, or negative electrode, of a lithium-sulfur cell requires lithium. During the discharge of a lithium-sulfur cell, lithium is dissolved from the anode surface into an electrolyte. This electrolyte (for example, a molten or liquid alkali metal polysulfide salt) is transported through a porous separator to a cathode (positive electrode during cell discharge), which comprises a polysulfide (for example, S8). Upon reaching the cathode, the lithium ions progressively reduce the polysulfide to a lithium-sulfur compound (for example, Li₂S₃).The chemical changes are reversed when the lithium-sulfur cell is recharged. The light weight and high energy density of lithium-sulfur cells make lithium-sulfur batteries good candidates for automotive propulsion systems and other electrically consuming devices. The fundamental mechanism responsible for battery capacity loss due to electrode material failure in its cells is the loss of electrical contact with conductive material and the creation of new surfaces that irreversibly consume the active lithium, forming new solid electrolyte interfaces. Both problems reduce the effective cycle life of a battery. A more efficient method or material for utilizing silicon or tin in the negative electrodes of lithium-ion cells remains a need. SUMMARY OF THE INVENTION The present invention is based on the objective of providing an improved electrochemical lithium-ion or lithium-sulfur secondary cell or battery. This problem is solved by the subject matter of the independent claims. Advantageous embodiments of the present invention are described in the dependent claims. According to embodiments of this invention, an improved negative electrode material for a lithium battery is formed by combining elemental silicon (a metalloid element) with tin and with another metal element as mixed but immiscible, separate solid phases. To be combined with silicon and tin, the second metal element is selected such that the diffusion of lithium into the mixture is incorporated and that it is essentially immiscible with both the silicon and the tin in the solid state. For example, elemental aluminum, copper, or titanium can be combined with silicon and tin in embodiments of this invention. Aluminum is preferred. In a preferred embodiment, a particulate composite material or composite material of silicon, tin, and aluminum (or a sputtered film composite material) is formed in which the silicon, aluminum, and tin are each present in separate phases in each particle of the composite material. The aluminum and tin phases are electrically conductive, and each of the three phases is receptive to the insertion and extraction of lithium atoms.The composite material is formed with a three-phase or multi-phase structure, the length or diameter of which of the characteristic phase (or the characterizing dimension for the phase in the composite material) is nanometers to micrometers, and this is achieved by regulating the synthesis process to produce the sizes of the mixed phases such that they are below the critical size for the generation of microcracks as a result of the repeated insertion of lithium into the mixed phases. In a preferred embodiment, confined particulate architectures are formed in which island-like amorphous silicon phases are dispersed in a matrix (or boundary layer) consisting of a tin phase and a phase of the second metal element (aluminum, silicon, or tin). Such a microstructure provides several advantages: (1) the tin phase and the aluminum phase are each electrically conductive, allowing electrons to reach the island-like silicon phase particles, which can hold a large number of lithium ions; (2) the diffusion of lithium in tin and aluminum (or another metal element selected for use in combination) is much faster than in silicon, which can reduce the concentration gradient of lithium ions through the larger composite material particles of silicon, tin, and aluminum, thereby reducing diffusion-induced stress and mitigating the fracture of the larger composite material particles.(3) If a crack is induced in the composite material, the relatively soft matrix phases of aluminum and tin tend to absorb the elastic stress energy and prevent microcracks from propagating, and (4) the immiscibility of silicon, aluminum, and tin and their phase separation minimize electrochemical sintering and thereby prevent particle coalescence, which would otherwise lead to rapid mechanical degradation of the electrode material. A thin layer of naturally formed oxide at the interfaces of the silicon phase and the metal phases (especially on aluminum) can also act as a passivation layer, improving Coulombic efficiency, preventing electrolyte degradation, and facilitating charge transfer to the surface of the composite electrode material. Phase-separated particle composites can be produced, for example, by rapid solidification processes (e.g., melt spinning) from a homogeneous (or uniformly dispersed) liquid mixture of elemental aluminum, tin, and silicon. In another example, phase-separated composites can be formed by co-sputtering separate sources of aluminum, tin, and silicon and co-depositing phase-separated mixtures of aluminum, tin, and silicon in predetermined ratios as an electrode film on a suitable surface, such as a copper current collector. If the sputtered deposition is atomically uniform, phase separation of the silicon, tin, and second metal element can be achieved by heating the substrate (e.g., to approximately 500 °C) or by another post-heat treatment process. According to the invention, a phase-separated composite material is produced in which the composite material consists of 50 atomic% silicon, 25 atomic% tin and 25 atomic% of a second metal, wherein the second metal element is selected from the group consisting of aluminium, copper and titanium. According to embodiments of the invention, the mechanical degradation that occurs when pure tin or pure silicon alone is used for lithium insertion is mitigated by fine-tuning the Si / Sn / Al atom ratio of the tin-silicon-aluminum composite material. At suitable Si / Sn / Al ratios, phase separation occurs with clusters of the amorphous silicon phase embedded in matrix phases of crystalline or amorphous tin and crystalline or amorphous aluminum. The resulting negative electrode materials exhibit significant improvements in charge storage capacity for lithium, along with excellent cycling stability. Thus, according to embodiments of the invention, phase-separated composite materials made of silicon, tin, and aluminum (or another second metal element) are formed as relatively thin layers on a suitable current collector foil or film for use as the negative electrode material in cells of a lithium-ion battery or a lithium-sulfur battery. Therefore, by using this phase-separated combination of silicon, tin, and aluminum, the lithium insertion capacity of each cell is increased, thereby improving the volumetric and / or gravimetric capacity of lithium-ion batteries or lithium-sulfur batteries. Further tasks and advantages of the invention will become clear from the detailed description of the working methods of embodiments of the invention, which are given in this description. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an enlarged schematic representation of some electrochemical cells of an exemplary lithium-ion battery arrangement. Each cell comprises a thin, rectangular negative electrode, which may include the phase-separated composite material of silicon, tin, and a second metal of this invention, a similarly shaped positive electrode, and a separator arranged between the electrodes. Fig. 2 is a more highly magnified exploded view of one of the electrochemical cells shown in Fig. 1. Fig. 2 also shows the metal current collectors that support the corresponding electrode materials. The cell elements are shown separately for illustration but are actually in compressed side-by-side contact, and the electrode materials are formed on or bonded to their respective current collectors.Figure 3 is a schematic representation based on a scanning electron microscopy (SEM) image of a silicon-tin composite material sample. The SEM image was labeled to illustrate the surface morphologies of a representative phase-separated silicon-tin-aluminum composite (e.g., a Si50Sn25Al25 composition, where the subscripts indicate atomic percent values ​​of the component). The original silicon-tin composite material sample was formed by sputtering silicon and tin from separate sputtering targets to form a film on a copper strip substrate. Silicon can be seen as island-like phases in a matrix of the aluminum and tin phases. Figure 4 is a plot of specific capacity (mAh / g) on ​​the left vertical axis and coulombic efficiency (CE) on the right vertical axis.Cycle count up to approximately 500 cell cycles, horizontal axis, for a composite material of composition Si50Sn25Al25 as the anode material in a half-cell using pure lithium as the counter electrode. The electrolyte solution was 1 M LiPF6 / ethylene carbonate and dimethyl carbonate (1:1 V / V) with 10% fluoroethylene carbonate additive. Cycling was performed at 25 °C. The solid line represents the data points for specific charge capacity (mAh / g). The long-short dashed line represents the data points for specific discharge capacity (mAh / g). And the dashed line of equal length represents the data points for CE. Fig. 5 is a graph of specific capacity (mAh / g), left vertical axis, and CE, right vertical axis, vs.Cycle count up to approximately 500 cell cycles, horizontal axis, for a composite material of composition Si50Sn25Cu25 as the anode material in a half-cell using pure lithium as the counter electrode. The electrolyte solution was 1 M LiPF6 / ethylene carbonate and dimethyl carbonate (1:1 V / V) with 10% fluoroethylene carbonate additive, and cycling was performed at 25 °C. The solid line represents the data points for specific charge capacity (mAh / g). The long-short dashed line represents the data points for specific discharge capacity (mAh / g). And the dashed line of equal length represents the data points for CE. Fig. 6 is a graph of specific capacity (mAh / g), left vertical axis, and CE, right vertical axis, vs.Cycle count up to approximately 500 cell cycles, horizontal axis, for a composite material of composition Si50Sn25Ti25 as the anode material in a half-cell using pure lithium as the counter electrode. The electrolyte solution was 1 M LiPF6 / ethylene carbonate and dimethyl carbonate (1:1 V / V) with 10% fluoroethylene carbonate additive, and cycling was performed at 25 °C. The solid line represents the data points for specific charge capacity (mAh / g). The long-short dashed line represents the data points for specific discharge capacity (mAh / g). And the dashed line of equal length represents the data points for CE. Fig. 7 is a graph of specific capacity (mAh / g), left vertical axis, and CE, right vertical axis, versus cycle count up to approximately 2000 cell cycles, horizontal axis, for further cycling of the composite material from Fig.4. A Si50Sn25Al25 composite material was used as the anode material in a half-cell with pure lithium as the counter electrode, and cycling was performed at 25 °C. The solid line represents the data points for the specific charge capacity (mAh / g). The long-short dashed line represents the data points for the specific discharge capacity (mAh / g). And the dashed line of the same length represents the data points for CE. DESCRIPTION OF PREFERRED EXECUTION FORMS An exemplary and generalized representation of a lithium-ion battery 10 is shown in Fig. 1. The lithium-ion battery 10 shown here comprises several thin, rectangular electrochemical battery cells 12, each enclosed by metallic current collectors. The electrochemical battery cells 12 are stacked side-by-side in a group configuration and, in this example, connected in parallel. A lithium-ion battery 10 can be formed from many identical electrochemical cells connected in series or in parallel to create a lithium-ion battery that has the voltage and current capacity required for a particular application. It should be understood that the lithium-ion battery 10 shown here is only a schematic representation.Figure 1 is presented to show the relative position and physical interactions of the various components that form the electrochemical battery cells 12 (i.e., the electrodes and the separator); it is not intended to specify the relative sizes of the components of the electrochemical battery cells, to define the number of electrochemical battery cells 12 in the lithium-ion battery 10, or to limit the wide variety of structural configurations that the lithium-ion battery 10 can assume. The electrochemical cell 12 (one shown), contained in the lithium-ion battery 10, comprises a negative electrode 14, a positive electrode 16, and the separator 18, which is located between the two opposing electrodes 14, 16. The negative electrode 14, the positive electrode 16, and the separator 18 are each moistened with a liquid electrolyte solution that enables the transport of lithium ions between the electrodes 14, 16. A metallic current collector 20 of the negative electrode (typically copper), comprising a negative terminal 22, is located between the immediately adjacent electrodes 14 of neighboring electrochemical cells 12. Similarly, a positive-side metallic current collector 24 (typically aluminum), comprising a positive terminal 26, is located between adjacent positive electrodes 16.The negative pole tab 24 is electrically connected to a negative terminal 28, and the positive pole tab 24 is electrically connected to a positive terminal 30. Each electrode material 14, 16 is typically formed on or bonded to its corresponding metallic current collector 20, 24. An applied compressive force typically presses the metallic current collectors 20, 24 and their electrodes 14, 16 against the separator 18 to achieve intimate interfacial contact between adjacent contacting components. The negative terminal 28 and the positive terminal 30 are connected to an electrically consuming load device 50. For example, a suitable battery pack comprising many similar individual cells can be provided to supply energy to an electric drive motor to power the wheels of a motor vehicle.In such a battery pack, many cells are connected in groups in an electrically parallel arrangement to provide a suitable energy capacity, and many groups are connected in series to provide a suitable electrical voltage potential. An exploded view of the electrochemical battery cell 12 and its associated metallic current collectors 20, 24 is generally shown in Fig. 2. The negative electrode 14 comprises an inner surface 32 and an outer surface 34 relative to the position of the separator 18. The positive electrode 14 similarly comprises an inner surface 36 and an outer surface 38. The inner surface 32 of the negative electrode 14 may, but is not required to, comprise a larger two-dimensional surface area than the inner surface 36 of the positive electrode, as shown. When assembled to form the electrochemical battery cell 12, the inner surfaces 32, 36 of the negative and positive electrodes 14, 16 face each other and are pressed against a negative-side main surface 40 and a positive-side main surface 42 of the separator 18, respectively.Such a pressing action generally occurs uniformly along the entire interface of the main side surfaces 40, 42 of the separator 18 and the corresponding portions of the inner surfaces 32, 36 of the electrodes 14, 16. The negative-side metallic current collector 20 is formed on or connected to the outer surface 34 of the negative electrode 14, and the positive-side metallic current collector 24 is formed on or electrically connected to the outer surface 38 of the positive electrode 16. In many embodiments of this invention, a tin-silicon composite material is formed as the negative electrode material directly on the surfaces of a copper current collector 20 of the negative electrode.Both metallic current collectors 20, 24 engage the outer surfaces 34, 38 of their respective electrodes over a considerable interface surface area to facilitate the efficient collection and conduction of free electrons. In many lithium-ion batteries, the elements of electrochemical cells 12 are made of materials that are generally thin and flexible. As an illustrative example, a typical thickness (T in Fig. 2) of the electrochemical cell 12, extending from the outer surface 34 of the negative electrode 12 to the outer surface 38 of the positive electrode 16, can be 80 µm to about 350 µm. Each electrode 14, 16 can be about 30 µm to 150 µm thick, and the separator 18 can be about 20 µm to 50 µm thick. The metallic current collectors 20, 24 can be about 5 µm to 20 µm thick. The relatively thin and flexible nature of the elements of the electrochemical cell 12 and their connected metallic current collectors 20, 24 allows them to be rolled, folded, bent or otherwise incorporated into a variety of lithium-ion battery configurations, depending on design specifications and spatial constraints.The lithium-ion battery 10 can, for example, comprise a series of separate electrochemical cells 12 that have been manufactured, cut, arranged and stacked on top of each other, or in an alternative embodiment, the cells 12 can be derived from a continuous layer that has been folded over many times. While lithium-ion batteries have been continuously developed and used, for example to power traction motors and the like for motor vehicles, lithium-sulfur batteries are only now being considered for such applications. As described, lithium-sulfur cells also use a lithium-containing negative electrode (anode) and electrode material that functions electrochemically like the negative electrode of a lithium-ion cell or battery. Accordingly, the silicon-tin-second metal element compositions and microstructures further described in this paper are suitable for lithium intercalation, regardless of whether the negative electrode material is used in a lithium-ion battery or in a lithium-sulfur battery.When a negative electrode is manufactured with a layer of the silicon-tin-aluminum (or other second metal) composite material of this invention as the negative electrode material, it is necessary to ensure the introduction of a predetermined amount of lithium into the electrode materials of the cell. In a preferred embodiment, a specified amount of lithium can be incorporated (lithiated) into the silicon-tin composite material, for example, by electrochemical insertion, electroplating, vacuum deposition, or physical contact with lithium metal in the presence of a suitable electrolyte. In another embodiment, a suitable amount of lithium can be introduced into the sulfur-containing positive electrode material before the elements of the lithium-sulfur cell are assembled.During an initial charge of the assembled cell or battery, lithium would be transported through the electrolyte and inserted into the negative electrode material made of silicon-tin composite material. Embodiments of this invention are aimed at creating higher current capacities and more durable materials for the negative electrodes of electrochemical lithium-ion cells. For this purpose, phase-separated composite materials made of silicon, tin, and a second metal, for example, aluminum, copper, or titanium, are produced. Composite material compositions of 50 atomic percent silicon, 25 atomic percent tin, and 25 atomic percent of a second metal in elemental form (to complement the tin) were fabricated. The second metals were aluminum, copper, or titanium. These composite materials are designated Si50Sn25Al25, Si50Sn25Cu25, and Si50Sn25Ti25, respectively. The corresponding composite materials were formed by co-deposition as three-element composite thin films in a Gamma 1000 sputtering system (Surrey Nanosystems, UK). In each fabrication, a roughened copper foil was used to ensure good adhesion between the sputtered Si-Sn-second-metal thin films and the copper current collector. The deposition plasma was generated for each component material (Si, Sn and Al or Cu or Ti) using RF (for silicon) or DC energy (for the metal elements), applied to three magnetron guns under an argon current of 14 scm3.The deposition rates for silicon, tin, and the second metal element were separately regulated to achieve the different atomic ratios of these elements specified above. The dynamic pressure during film growth was 3 mTorr, and the substrate was kept at room temperature. Ex-situ X-ray diffraction (XRD) was used to investigate the structures of the thin films deposited on the Cu current collectors. All samples were analyzed using Cu-Kα radiation in a Bruker AXS general area detector diffractometer (GADDS) system. Diffraction images were acquired over a 5-minute period using a 0.5 mm collimator and a sample-to-detector distance of 150 mm. The composition of each sample pad was determined by electron beam microanalysis (ESMA), while selected samples were characterized using a JEOL-2100F AC transmission electron microscope operating at 200 kV. Scanning transmission electron microscopy (RTEM) images were acquired using a wide-field dark-field ring detector (HAADF). All electrochemical experiments were performed in button cells inside an argon-filled glove box at ambient temperature (25 °C). Pure lithium metal was used for the counter electrode in the half-cell tests. The electrolyte solution was 1 M LiPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 V / V) with 10% fluoroethylene carbonate additive. A Celgard 3501 film (1 µm thick microporous polypropylene film with 40% porosity) was used as a separator. Galvanostatic tests for all samples were performed using an Arbin BT-2000 battery test station at a cycling voltage between 10 mV and 1.5 V (relative to a Li / Li+ electrode). The XRD results included the strong Cu diffraction peaks observed from the substrate and showed several Sn peaks, indicating that the Sn phase was crystalline. Depending on the specific sample, strong aluminum, copper, or titanium peaks were also observed. No Si diffraction peaks were detected, indicating the amorphous nature of the Si. This was expected, as the deposition temperature is too low for Si to develop a crystalline phase. No peaks representing a different Si-Sn, Si-Al, Si-Cu, or Si-Ti phase were observed in any of the sputtered samples examined, clearly demonstrating that the Si and the two metal constituents were phase-separated, consistent with the known immiscibility of Si, Sn, Al, Cu, and Ti.This nanostructure, induced by phase separation, is critical for significantly improving its electrochemical performance. The overall mechanism is described in more detail in this report. Based on the well-known Scherrer equation, the average Sn and Al crystallite size, estimated from X-ray diffraction spectra, was about 20 to 50 nm. Fig. 3 is a SEM image of a sputtered silicon-tin composite material, labeled and schematically marked to show the shapes and locations of the island-like silicon phases and the tin and aluminum matrix phases. The dark, island-like clusters are the silicon grains. The lighter boundary phases surrounding the silicon grains are a combination of separate shell-like microstructures formed by the separate tin and aluminum phases. During composite formation, the aluminum and tin tend to wet the silicon particles, forming a metal oxide layer at the phase interfaces. The presence of the metal oxide at the interfaces improves the efficiency of the first charge-discharge cycle as well as subsequent cycle stability.The SEM image is also marked with an arbitrarily applied fine white line drawn through the matrix phases from the upper to the lower part of the image. This applied line indicates an undesirable microcrack in the composite material. This microcrack is not present and was avoided by the depicted composition and microstructure. Lithium diffuses more rapidly into the tin and aluminum than into the silicon, allowing for a more uniform distribution of lithium within the composite material. As a result of a lower lithium concentration gradient, less stress is generated in the composite structure. Microcracks are undesirable in the negative electrode material because they impair the material's function. A composite material with the composition Si50Sn25Al25 was tested as the anode material in a half-cell using pure lithium as the counter electrode. The electrolyte solution was 1 M LiPF6 in ethylene carbonate and dimethyl carbonate (1:1 V / V) with 10 vol% fluoroethylene carbonate additive, and cycling was performed at 25 °C. The cell was operated to determine the specific capacity of the Si50Sn25Al25 composition for intercalation with lithium (the specific charge capacity in milliamperes per hour per gram of lithium during charging of the Si50Sn25Al25 composition). In the reverse cycle, the cell was operated to remove the lithium from the Si50Sn25Al25 composition. Figure 4 is a graph of specific capacity (mAh / g) on ​​the left vertical axis and CE (Coulomb efficiency) on the right vertical axis.Cycle count up to approximately 500 cell cycles, horizontal axis, for the composite material of composition Si50Sn25Al25 as anode material in a half-cell, using pure lithium as the counter electrode. The solid line represents the data points for the specific charge capacity (mAh / g). The long-short dashed line represents the data points for the specific discharge capacity (mAh / g). And the dashed line of the same length represents the data points for CE. It can be seen that the Coulombic efficiency of the cell operation remained above 99.5% after 10 cycles. And the specific capacity of the composite material remained between 1200 and 1600 mAh / g during charging and discharging over the 500 cycles. Figure 7 presents additional data obtained after further cycling up to 2000 charge / discharge cycles for the Si50Sn25Al25 composition prepared above as the anode material in a half-cell using pure lithium as the counter electrode. After the first several cycles, the specific capacity values ​​remained at approximately 1180 mAh / g during charge and discharge cycles up to about 1600 cycles. The Coulombic efficiency remained above 99.5% after five cycles. A composite material of composition Si50Sn25Cu25 was tested as the anode material in a half-cell using pure lithium as the counter electrode. The electrolyte solution was 1 M LiPF6 in ethylene carbonate and dimethyl carbonate (1:1 V / V) with 10 vol% fluoroethylene carbonate additive, and cycling was performed at 25 °C. The cell was operated to determine the specific capacity of the Si50Sn25Cu25 composition for intercalation with lithium (the specific charge capacity in milliamperes per hour per gram of lithium during a charge of the Si50Sn25Al25 composition). In the reverse cycle, the cell was operated to remove the lithium from the Si50Sn25Cu25 composition. Figure 5 is a graph of specific capacity (mAh / g) on ​​the left vertical axis and CE (Coulomb efficiency) on the right vertical axis.Cycle count up to approximately 200 cell cycles, horizontal axis, for the composite material of composition Si50Sn25Cu25 as the anode material in a half-cell using pure lithium as the counter electrode. The solid line represents the data points for the specific charge capacity (mAh / g). The long-short dashed line represents the data points for the specific discharge capacity (mAh(g). And the dashed line of the same length represents the data points for CE. It can be seen that the Coulombic efficiency of the cell operation remained above 99% after 20 cycles. And the specific capacity of the composite material started at a level of approximately 800 mAh / g during charging and discharging. Then it experienced a continuous decrease as an intermetallic compound formed between the copper and tin. A composite material of the composition Si50Sn25Ti25 was tested as the anode material in a half-cell using pure lithium as the counter electrode. The electrolyte solution was 1 M LiPF6 / ethylene carbonate and dimethyl carbonate (1:1 V / V) with 10 vol% fluoroethylene carbonate additive, and cycling was performed at 25 °C. The cell was operated to determine the specific capacity of the Si50Sn25Ti25 composition for lithium intercalation (the specific charge capacity in milliamperes per hour per gram of lithium during a charge of the Si50Sn25Ti25 composition). In the reverse cycle, the cell was operated to remove the lithium from the Si50Sn25Ti25 composition. Figure 6 is a graph of specific capacity (mAh / g) on ​​the left vertical axis and Coulomb efficiency (CE) on the right vertical axis.Cycle count up to approximately 200 cell cycles, horizontal axis, for the composite material of composition Si50Sn25Cu25 as anode material in a half-cell using pure lithium as the counter electrode. The solid line represents the data points for the specific charge capacity (mAh / g). The long-short dashed line represents the data points for the specific discharge capacity (mAh / g). And the dashed line of the same length represents the data points for CE. It can be seen that the Coulombic efficiency of the cell operation remained above 99% after 50 cycles. And the specific capacity of the composite material started at around 800 mAh / g during both charging and discharging. Then the specific capacity experienced a continuous deterioration due to the formation of an intermetallic compound between the titanium and the tin. The experimental data presented in Figures 4, 5, 6 to 7 show that the tested combination of silicon, tin, and aluminum performed best among the three combinations tested. The tests demonstrate the importance of the silicon-tin-second metal element composite composition in maintaining its phase-separated nanostructure and the suitable oxide layer that forms on the material surfaces. In the illustrative examples above, the negative electrode composite materials were produced by sputtering the individual components onto a copper foil current collector. The phase-separated silicon-tin-second metal compositions can also be produced by a rapid solidification process from a homogeneous melt with suitable proportions of silicon, tin, and aluminum (or the like). In general, it is preferred to form composite materials of about 20 to 80 atomic percent silicon, about 20 to 60 atomic percent tin, and about 1 to 30 atomic percent of a lithium-receptive metal such as aluminum, copper, titanium, or another suitable metal that is immiscible with silicon and tin. The process can be carried out, for example, as follows, using the example of a silicon-tin-aluminum composite material. 1.Silicon, tin, and aluminum are fused together in a predetermined atomic ratio, as specified above in this description. 2. The melt is progressively solidified rapidly to form particles, flakes, or ribbons. 3. The particles are comminuted, for example, by cryogenic sphere milling at a suitably low temperature below 0 °C and down to -30 °C in an inert atmosphere to avoid oxidation of the particles, to form generally uniformly shaped particles of 1 to 4 micrometers or so (or less) in their largest dimension. 4. In some embodiments, the particles may be annealed or heat-treated, if necessary, to induce phase separation by forming nanoscale islands of amorphous silicon phases embedded in a matrix of separated phases of tin and aluminum.Phase-separated composite material particles of silicon, tin, and aluminum are considered the active material for a negative electrode of a lithium-ion cell. 5. The active material particles are bonded to a suitable metal current collector, preferably a copper current collector, during the formation of a negative electrode. The active electrode material particles can be mixed, for example, with a suitable polymeric binder, such as polyvinylidene fluoride (PVDF) or sodium alginate, and carbon black (a conductor) in a weight ratio of, for example, 80:10:10. An inert liquid vehicle can be used temporarily to distribute the mixture over one or both opposing surfaces of a thin current collector strip. The liquid vehicle is then removed, and the mixture, along with the polymeric binder, is bonded to the collector film surfaces.The electrical conductivity of the silicon-tin-aluminium composite material is further increased by the carbon black particles. Thus, the phase-separated films are formed in a suitable manner over a predetermined area and to a specific thickness on a copper current collector for use as negative electrode material in electrochemical lithium-ion cells or electrochemical lithium-sulfur cells. Lithium can be introduced into the silicon-tin-aluminum composite material during electrode fabrication, initial charging, or other cell operation. The total amount of negative electrode material and its lithium content are selected to provide the desired electrode capacity. Embodiments of the invention have been described for illustrative purposes and not to limit the scope of the invention.

Claims

An electrochemical lithium-ion or lithium-sulfur secondary cell or battery comprising a negative electrode composition utilizing lithium; wherein the lithium is drawn into the negative electrode composition during charging of the cell or battery and is withdrawn from the negative electrode composition during discharging of the cell or battery; the negative electrode material comprising a composite material consisting of silicon, tin, and a second metallic element selected from the group consisting of aluminum, copper, and titanium, wherein the composite material is further characterized in that the silicon, tin, and the second metal are present separately in different phases, the tin phase and the phase of the second metallic element being crystalline or amorphous, and the silicon phase being amorphous;wherein the composite material of silicon, tin and the second metal element is further characterized by nanoscale islands of amorphous silicon phase dispersed in a matrix of a tin phase and a phase of the second metal element, wherein the composite material consists of 50 atomic% silicon, 25 atomic% tin and 25 atomic% of the second metal. Electrochemical lithium-ion or lithium-sulfur secondary cell or battery according to claim 1, in which the second metal element is aluminium. Electrochemical lithium-ion or lithium-sulfur secondary cell or battery according to claim 1, wherein the composite material of silicon, tin and the second metal element is characterized by crystals of the tin phase and crystals of the phase of the second metal element, each having a size in the range of twenty nanometers to fifty nanometers. Electrochemical lithium-ion or lithium-sulfur secondary cell or battery according to claim 1, wherein the composite material of silicon, tin and the second metal element was formed as a tightly adhering film by sputtering silicon, tin and the second metal element onto a surface of a metal current collector for the negative electrode material, wherein the sputtered film has a thickness of up to five micrometers. Electrochemical lithium-ion or lithium-sulfur secondary cell or battery according to claim 2, wherein the composite material of silicon, tin and aluminium was formed as a tightly adhering film by sputtering silicon, tin and aluminium onto a surface of a metal current collector for the negative electrode material, wherein the sputtered film has a thickness of up to five micrometers. Electrochemical lithium-ion or lithium-sulfur secondary cell or battery according to claim 1, wherein the composite material of silicon, tin and the second metal element was formed by rapid solidification of a molten liquid of silicon, tin and the second metal element into solid particles of the phase-separated composite material of silicon, tin and the second metal element, wherein the solid particles were reduced in size to one to five micrometers by ball milling at a temperature of below 0 °C and down to -30 °C in an inert atmosphere and then mixed with a polymeric binder and bonded to a metal current collector for the negative electrode material. Electrochemical lithium-ion or lithium-sulfur secondary cell or battery according to claim 1, wherein a composite material of silicon, tin and aluminium was formed by rapid solidification of a molten liquid of silicon, tin and aluminium to solid particles of the phase-separated composite material of silicon, tin and aluminium, wherein the solid particles were reduced in size to one to five millimeters and then mixed with a polymeric binder and carbon black and bonded to a metal current collector for the negative electrode material. Electrochemical lithium-ion or lithium-sulfur secondary cell or battery according to claim 1, wherein the negative electrode material, prior to an initial charge of the cell or battery, comprises a composite material of silicon, tin and a second metal element containing incorporated lithium. Electrochemical lithium-ion or lithium-sulfur secondary cell or battery comprising a negative electrode composition and a positive electrode composition; wherein lithium is drawn into the negative electrode composition and drawn out of the positive electrode composition by transport of lithium through a lithium-containing electrolyte during charging of the cell or battery, and wherein lithium is drawn out of the negative electrode composition and drawn into the positive electrode composition by transport of lithium through a lithium-containing electrolyte during discharging of the cell or battery;wherein the negative electrode material comprises a composite material consisting of silicon, tin and a second metal element selected from the group consisting of aluminum, copper and titanium, wherein the composite material is further characterized in that the silicon, the tin and the second metal element are present separately in different phases, the tin phase and the phase of the second metal element are crystalline or amorphous and the silicon phase is amorphous, wherein the composite material of silicon, tin and the second metal element is further characterized by nanoscale islands of amorphous silicon phase dispersed in a matrix of a tin phase and a phase of the second metal element, wherein the composite material consists of 50 atomic% silicon, 25 atomic% tin and 25 atomic% of the second metal.

Images