ELECTRODE, ENERGY STORAGE DEVICE AND METHOD

Abstract

Electrode for an energy storage device which comprises a powder of particles (26) comprising amorphous, micro- or nano-crystalline coated or uncoated silicon oxynitride having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen.

Claims

1. Electrode (34) for an energy storage device (32) which comprises a powder of particles (26) comprising amorphous, micro- or nano-crystalline silicon oxynitride, characterized in that said powder of particles (26) comprises coated or uncoated silicon oxynitride having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen.

2. Electrode (34) according to claim 1, characterized in that 0.03≤x+y<0.3, or 0.03≤x+y<0.2, or 0.1≤x+y<0.3, or 0.1≤x+y<0.2.

3. Electrode (34) according to claim 1 or 2, characterized in that said SiN.sub.xO.sub.y particles (26) have a maximum transverse dimension of 150 nm in a coated or uncoated state.

4. Electrode (34) according to claim 1 or 2, characterized in that said SiN.sub.xO.sub.y particles (26) have a maximum transverse dimension of up to 10 μm in a coated or uncoated state.

5. Electrode (34) according to any of the preceding claims, characterized in that the SiN.sub.xO.sub.y particles comprise 0-60 atomic-% of one or more elements other than silicon and nitrogen and oxygen.

6. Electrode (34) according to any of the preceding claims, characterized in that said SiN.sub.xO.sub.y particles (26) have a lithium content in the range of 0 to 60 atomic-%.

7. Electrode (34) according to any of the preceding claims, characterized in that said SiN.sub.xO.sub.y particles (26) contain at least one of the following modifying elements: phosphorus (P), boron (B), carbon (C), sulphur (S), selenium (Se), arsenic (As), tin (Sn), magnesium (Mg), aluminium (Al), iron (Fe), germanium (Ge) and/or antimony (Sb).

8. Electrode (34) according to any of the preceding claims, characterized in that said powder of particles comprises aggregates of individual SiN.sub.xO.sub.y particles.

9. Electrode (34) according to any of the preceding claims, characterized in that said SiN.sub.xO.sub.y particles (26) are at least partially coated and have a core region comprising silicon oxynitride having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen, and at least one continuous or non-continuous shell region (28) comprising inorganic and/or organic material.

10. Electrode (3) according to any of the preceding claims, characterized in that it comprises a binder and/or one or more conductive additives.

11. Energy storage device (32), characterized in that it comprises at least one electrode (34) according to any of the preceding claims.

12. Energy storage device (32) according to claim 11, characterized in that it is a battery, such as a Li-ion battery.

13. Energy storage device (32) according to claim 11 or 12, characterized in that it comprises an electrolyte additive that enhances a first cycle lithiation of said SiN.sub.xO.sub.y particles (26), by providing a surface electrolyte interface (SEI) layer that facilitates the lithiation of SiN.sub.xO.sub.y particles (26).

14. Energy storage device according to claim 13, characterized in that said electrolyte additive is at least one of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC).

15. Energy storage device (32) according to claim 11 or 12, characterized in that it comprises an electrolyte additive that enhances a first cycle Coulombic efficiency of said SiNxOy (26), by providing an additional source of lithium that is arranged to be incorporated into the material during cycling.

16. Method for producing an electrode (34) according to any of claims 1-10, characterized in that it comprises the steps of mixing a powder of particles (26) comprising coated or uncoated silicon oxynitride having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen, with a binder, optionally one or more additives, such as one or more electrically conductive additives, and a solvent, such as water, with or without pH adjustments, and printing or coating said mixture on a surface of a current collector and drying to form an electrode (34).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended schematic figures where;

[0072] FIG. 1 shows a device for producing SiN.sub.xO.sub.y particles,

[0073] FIG. 2 shows a coated SiN.sub.xO.sub.y particle,

[0074] FIG. 3 shows an electrical energy storage device, namely a battery comprising an electrode according to an embodiment of the invention and electrolyte,

[0075] FIG. 4 is a flow chart showing the steps of a method described herein, and

[0076] FIGS. 5-7 show microscopy images of SiN.sub.xO.sub.y particles according to embodiments of the invention.

[0077] It should be noted that the drawings have not necessarily been drawn to scale and that the dimensions of certain features may have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION OF EMBODIMENTS

[0078] FIG. 1 shows a device 10 for producing a powder comprising amorphous, micro- or nano-crystalline silicon oxynitride particles having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen by homogeneous thermal decomposition or reduction of reactant gases 12 containing silicon and nitrogen and oxygen.

[0079] The embodiment illustrated with reference to FIG. 1 involves the production of SiN.sub.xO.sub.y in the device 10. The device 10 may however alternatively be used to produce silicon nitride particles that do not contain the oxygen, whereby a reactant gas containing oxygen is not supplied to the device 10 during the production of the silicon nitride particles. Instead, the produced silicon nitride particles are subsequently exposed to an oxygen-containing atmosphere to produce a powder of silicon oxynitride particles having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen.

[0080] The device 10 comprises a reactor 14 having a reaction chamber 16 with one or more inlets for the reactant gases 12, located at the top of the device 10 for example to obtain a descending reactant gas flow. The reactor 14 may be a Free Space Reactor having stainless steel, silicon carbide or quartz walls for example, which is arranged to decompose the reactant gas 12 homogeneously in the gas phase and thus to grow the desired SiN.sub.xO.sub.y particles. Volatile by-products may be removed by gas flow through the reaction chamber 16.

[0081] Contrary to a multi-stage reactor, such as the one disclosed in U.S. Pat. No. 4,314,525, in the device 10, no seed particles are introduced into the reactor 14. Furthermore, particles are not grown on a substrate, such as a hot substrate or deposited on a wafer, such as a heated wafer, and no salt is used to produce the particles. In the method, deposition is carried out on particles floating in heated gas.

[0082] The device 10 also comprises means 18, such as heating coils, which are located around the outer wall of the reactor 14 in the illustrated embodiment, to heat the reactant gases 12 to a temperature sufficient for thermal decomposition or reduction of the reactant gases 12 to take place inside the reaction chamber 16. The reactant gases 12 are preferably pre-heated to a temperature that is just below the reaction temperature and then, when the reactant gases are in the reaction chamber 16, the temperature inside the reactor 10 provides the energy required so that the particles start forming. This produces particles with a narrow size distribution.

[0083] The reaction chamber 16 in the illustrated embodiment is constituted by a single wall constituted entirely by a porous membrane 20, such as a substantially cylindrical tube of material of suitable mechanical and chemical properties. It should be noted that the porous membrane 20 may be of any suitable shape, it may for example be in the form of an upright or inverted cone.

[0084] The device 10 may optionally comprise one or more inlets that are arranged to supply a primary gas 22, such as hydrogen or argon, through the porous membrane 20 to provide a protective inert gas boundary at the wall of the reaction chamber 16 to minimize or prevent the deposition of the material on the porous membrane 20 when the device 10 is in use. The one or more inlets may optionally also be used to supply a secondary gas through the porous membrane 20 to influence the thermal decomposition or reduction of the reactant gas 12 inside the reaction chamber 16. The expression “influence the thermal decomposition or reduction of the reactant gas inside the reaction chamber” as used in this document is intended to mean slow down, speed up, prevent, start, modify or change one or more chemical reactions taking place inside the reaction chamber 16. It is not however necessary for a reactor in which a method is carried out to comprise a porous membrane 20.

[0085] A silicon-containing reactant gas 12, such as monosilane (SiH.sub.4), which might or might not be diluted in hydrogen or with other gases such as Ar, may be supplied to the reaction chamber 16. Means 18 for heating the reaction chamber 16 raises the temperature of the silicon-containing reactant gas 12 to a point of thermal decomposition whereby the following reaction takes place and elemental silicon, is formed:

SiH.sub.4.fwdarw.Si+2H.sub.2

[0086] For monosilane this temperature is 400° C., however, for growth control the temperature of pyrolysis could be above this value. The reactant gas 12 may also contain one or more modifying gases, such as arsine, diborane, phosphine, boron trifluoride, trimethylboron or any other metal/organic/inorganic modifying gas, which may for example be added in the particles' nucleation and/or growth phase(s). The reactant gas 12 may for example contain a metal or lithium-containing gas, which is supplied during the particle nucleation phase, and/or after the particle nucleation phase. It should be noted that a modifying gas may additionally or alternatively be supplied through the porous membrane 20 in the illustrated embodiment.

[0087] Primary gas 22, such as hydrogen, nitrogen or argon is supplied to a chamber 24 outside the reaction chamber 16 that is delimited by the porous membrane wall 20. The reactor 14 is thereby divided into an outer chamber 24 for primary gas 22 and an inner reaction chamber 16 where a decomposition or reduction reaction takes places at a distance from the wall(s) of the reaction chamber 16. The primary gas 22 in the outer chamber 24 is namely arranged to pass through the porous membrane 20 from the outer chamber 24 to the near wall region of the reaction chamber 16. When the primary gas 22 enters the reaction chamber 16, the near wall region will be kept free of reactant gas 12 and thus unwanted wall depositions will be avoided.

[0088] Secondary gas may also be supplied to the chamber 24 outside the reaction chamber 16 that is delimited by the porous membrane wall 20. The secondary gas may be added in the particles' nucleation and/or growth phase(s). The secondary gas may for example contain a metal- or lithium-containing gas, which is supplied through the porous membrane during the particle nucleation phase, and/or after the particle nucleation phase but prior to their exposure to air.

[0089] Depending on the operation temperature and requirements for the finished product, the porous membrane 20 may comprise a metal alloy such as AISI316, Inconel, 253MA or HT800. The membrane may also be produced from porous sintered silicon-nitride Si.sub.3N.sub.4, porous silica SiO.sub.2, porous alumina Al.sub.2O.sub.3, graphite or any other suitable material.

[0090] It should be noted that the reaction chamber 16 dimensions may vary from having a maximum transverse dimension of a few millimetres to a few metres.

[0091] The thermal decomposition or reduction of the reactant gases 12 inside the reaction chamber 16 is controlled so as to produce a powder of SiN.sub.xO.sub.y particles which may subsequently form a core region 26 of a coated particle 30 as schematically shown in FIG. 2. The thermal decomposition or reduction of the reactant gases 12 inside the reaction chamber 16 may for example be controlled by adjusting the temperature, pressure, flow rate, heat capacity and/or composition, of the reactant gases 12 (and/or a reaction-influencing gas).

[0092] FIG. 2 shows a coated SiN.sub.xO.sub.y particle 30 comprising a core region 26 and a shell region 26 comprising one continuous shell. An electrode according to the present invention may comprise continuously or non-continuously coated SiN.sub.xO.sub.y particles 30 or a mixture of continuously and/or non-continuously coated, and uncoated SiN.sub.xO.sub.y particles. The coated particles 30 may be substantially spherical and may have a core region 26 that is substantially spherical.

[0093] The SiN.sub.xO.sub.y particles comprise coated or uncoated silicon oxynitride having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen. Different SiN.sub.xO.sub.y chemical compositions can be achieved by varying the ratio of the precursor gases. The chemical composition of the SiN.sub.xO.sub.y particles may be determined using energy-dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) analysis, for example.

[0094] An electrode according to the present invention may comprise aggregate of individual SiNxOy particles whereby each SiN.sub.xO.sub.y particle comprises at least one continuous or non-continuous shell region 28, or whereby a plurality of SiN.sub.xO.sub.y particles comprise at least one common continuous or non-continuous shell 28. The at least one continuous or non-continuous shell 28 may comprise one or more organic and/or inorganic materials. The at least one shell 28 may contain carbon.

[0095] A shell region 28 may comprise 3-100 monolayers of organic and/or inorganic material so as to be thin but mechanically robust.

[0096] The thermal decomposition or reduction of the reactant gases 12 inside the reaction chamber may be influenced by changing at least one of the following characteristics of the reactant gas and/or reaction-influencing gas: temperature, pressure, flow rate, heat capacity, composition, modifying element type(s) and/or amount(s), catalyst type(s) and/or amount(s), and/or concentration of one or more components of said gases. By changing at least one of the characteristics of the reactant gases and/or reaction-influencing gas, the thermal decomposition or reduction of the reactant gas inside the reaction chamber, and consequently the formation and/or growth of particles, and/or their morphology and/or crystallinity, may be controlled in order to obtain a final product having the desired characteristics.

[0097] For example, the temperature of the primary gas and/or secondary gas may be increased once particles have been formed in order to produce crystalline material. Alternatively, the temperature of the primary gas and/or secondary gas may be decreased to produce amorphous material. The amount of hydrogen in the primary gas and/or secondary gas may be increased to decrease the production of nuclei and thereby the total number of particles. The flow rate of the primary gas and/or secondary gas may be increased to promote turbulence inside the reaction chamber, or decreased to reduce turbulence, depending on which conditions are conducive to the production of the desired product.

[0098] The primary gas and/or secondary gas preferably has/have a high heat capacity to help provide uniform heating within the reaction chamber. This may however vary with the application since several decomposition reactions include intermediate reversible stages, whereby it may be advantageous to promote particle growth over particle formation. Such stages may be temperature dependent, and in such cases a controlled uneven temperature distribution is favourable.

[0099] The secondary gas may be supplied through the porous membrane simultaneously with the primary gas, periodically, continuously, intermittently, when desired, or in any combination of these ways during the use of a reactor. The primary gas and the secondary gas may be arranged to be supplied through the same pores, or through different pores in the porous membrane.

[0100] It should also be noted that the expressions “primary gas” and “secondary gas” as used in this document need not necessarily mean that said gases comprise just one type of gas.

[0101] A primary gas and/or a secondary gas may also comprise at least one catalyst gas. Furthermore, different primary gases and/or secondary gases may be used during the use of a reactor.

[0102] The actual dimensions of the components of the device 10 (such as the diameter or length of the reaction chamber tube or the shape of the reactor chamber) are not especially critical. In addition, operating parameters such as gas flow rates and operating temperatures can be established experimentally for different devices having different sizes and configurations.

[0103] The particles could be exposed to another gas contain modifying elements (such as oxygen and others) prior to the collection.

[0104] The method may be used to produce a high volume of powder of SiN.sub.xO.sub.y particles. The method is easy to scale up and it is possible to achieve continuous particle production while the reactor is in use.

[0105] FIG. 3 shows an energy storage device 32, namely a battery comprising an electrode 34 according to an embodiment of the invention, which constitutes an anode of the energy storage device 32. The energy storage device 32 also comprises a cathode 36 and electrolyte 38, which may be liquid, solid or a gel. Optionally, an electrical energy storage device according to the present invention may contain a separator 39.

[0106] FIG. 4 is a flow chart showing the steps of a method described herein. The method comprises the steps of supplying reactant gases containing silicon and nitrogen and oxygen to a reaction chamber of a reactor, heating the reactant gas to a temperature sufficient for thermal decomposition or reduction of the reactant gases to take place inside the reaction chamber to thereby produce a powder of particles comprising silicon oxynitride having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen.

[0107] Alternatively, the method may comprise the steps of supplying reactant gases containing silicon and nitrogen to a reaction chamber of a reactor, heating the reactant gas to a temperature sufficient for thermal decomposition or reduction of the reactant gases to take place inside the reaction chamber to thereby produce a powder of silicon nitride particles.

[0108] The silicon nitride particles may then be exposed to an oxygen-containing atmosphere to produce a powder of silicon oxynitride particles having a chemical formula SiN.sub.xO.sub.y, where 0.03≤x+y<1.3, whereby nitrogen makes up 10-99% of said x+y value with the balance being oxygen.

[0109] Optionally, either of these two methods may also comprise one or more of the following steps (which have been illustrated in dashed boxes in FIG. 4): supplying at least one gas containing a metal, such as lithium to the reaction chamber of the reactor, supplying at least one modifying gas to said reaction chamber of said reactor to modify the particles, coating the SiN.sub.xO.sub.y particles or silicon nitride particles with passivating material in the reaction chamber or in a different vessel, using the coated or uncoated SiN.sub.xO.sub.y particles to produce an electrode for an energy storage device, such as a Li-ion battery.

[0110] It should be noted that the steps of supplying reactant gases containing silicon and nitrogen and oxygen to a reaction chamber of a reactor, supplying at least one gas containing a metal, such as lithium to the reaction chamber of the reactor and supplying at least one modifying gas to said reaction chamber of said reactor to modify the particles do not have to be carried out in a particular sequence. An inert gas boundary is preferably, but not necessarily established before reactant gases and/or a secondary gas are supplied to the reaction chamber.

[0111] The method may also comprise at least one of the optional steps of pre-heating the reactant gases to a temperature below the reaction temperature before the reactant gases are supplied to the reaction chamber of the reactor and/or heat treating the particles after their production, in an oxygen-free atmosphere, such as an inert atmosphere or hydrogen-containing atmosphere. Alternatively, the method may comprise the step of exposing the produced particles to an oxygen-containing atmosphere or environment to provide SiN.sub.xO.sub.y particles which can optionally have a stochiometric or non-stochiometric silicon oxide shell.

[0112] The post-production heat treatment step may be carried out at a temperature of 600-1300° C. with a process time within 2-3600 seconds in the inert or hydrogen-containing atmosphere.

[0113] The post-production step may be carried out at the temperatures of 25-1300° C. with a process time within 2-3600 seconds in the oxygen-containing atmosphere.

[0114] An electrode may be fabricated using slurry-based processing in which the produced SiN.sub.xO.sub.y particles are mixed with a binder, optionally one or more additives, such as an electrically conductive additive, and a solvent, such as water, with or without pH adjustments, printed or coated on a surface of a current collector and dried to form an electrode.

[0115] The solids used for slurry preparation may comprise at least 2 weight-%, at least 5 weight-%, at least 10 weight-%, at least 20 weight-% , at least 30 weight-%, at least 40 weight-%, at least 50 weight-% or at least 60 weight-% of the SiN.sub.xO.sub.y particles.

[0116] FIG. 5 shows a scanning transmission electron microscopy (STEM) image taken using a 4-quadrant dark field (DF4) detector that detects the small fraction of electrons that are scattered outside of the bright field (BF) region, to the dark field (DF) region. The image shows the distribution of silicon, nitrogen and oxygen atoms in an uncoated silicon oxynitride particle according to an embodiment of the invention. The silicon oxynitride particle has a chemical formula SiN.sub.0.54O.sub.0.1 whereby x=0.54, y=0.1, and x+y=0.64. The atomic composition of the particle is 61% silicon, 33% nitrogen and 6% oxygen. Oxygen atoms are visible as a halo around the particle in the microscopy image. The silicon oxynitride particle is attached to another silicon oxynitride particle that is visible in the top right-hand corner of the image.

[0117] FIG. 6 shows a STEM image taken using a DF4 detector of another uncoated silicon oxynitride particle having the same chemical composition as the particle shown in FIG. 5. The silicon oxynitride particle is attached to another silicon oxynitride particle that is just visible on the right-hand side of the image.

[0118] FIG. 7 shows three STEM images which each show the distribution of either silicon, nitrogen or oxygen atoms in the uncoated silicon oxynitride particle shown in FIG. 5. The fourth image is taken using a DF4 detector.

[0119] Further modifications of the invention within the scope of the claims would be apparent to a skilled person.