Patent Application
20190263666
The present invention relates to rechargeable lithium ion batteries, often termed Li-ion batteries or secondary batteries, and typically used in handheld devices such as cellphones. More specifically, the invention relates to silicon anode material for said batteries, in the form of a method for production, use of a rotating reactor for the method and the particles per se.
Currently, a shift from carbon based anodes to silicon-based anodes for lithium ion rechargeable batteries take place. The reason is the increased capacity achievable. Graphite has a theoretical capacity of about 350-365 mAh/g graphite, which is better than several alternatives. However, silicon has a theoretical capacity of 4200 mAh/g when forming Li22Si5 and 3580 mAh/g when forming Li15Si4, which gives a large potential if conversion to silicon based anodes in lithium ion batteries is feasible.
The challenge of utilizing silicon as part of the active material is that silicon undergoes a large volume expansion when intercalating lithium ions. This expansion results in cracking and degradation of the material. Other problems involves formation of electrically disconnected active material, surface reaction between the silicon and the electrolyte forming an inactive brittle layer also referred to as the solid electrolyte interface (SEI). This SEI layer may also crack and peel off the silicon during release of the lithium ions, thereby exposing new silicon surface and the formation of a new inactive SEI layer. The continued SEI formation is both a challenge as it reduces the amount of active silicon material but also since the process consumes parts on the electrolyte. This process will ultimately result in a continued decrease of available active material and reduced capacity of the battery.
The method of thermally decomposing a gaseous silicon precursor to make silicon particles is a known established method, cf. Flagan et al., U.S. Pat. No. 4,642,227. However, utilizing this method results in a silicon powder with a too large size distribution. There have also been numerous attempts to introduce silicon as part of the active material within the anode, using different methods including decomposition of a silicon containing precursor, cf. Lee et al. US2016/0190570 A1. However, without being able to both control the size distribution and the surface chemistry of the particles upon contact with an electrolyte and intercalation and de-intercalation of lithium ions the particles will undergo destructive processes during cycling and ultimately break down.
The most successful attempts so far to produce silicon based anodes for lithium ion batteries are based on making small similar symmetrical silicon geometries, whereby each silicon geometry is filled and emptied at a similar rate in a battery, whereby the tension stress within each silicon geometry does not exceed the tensile strength of the silicon by having the size small. Such geometries have included bottom up grown structures such as silicon nano-particles, nano-wires, nano-tubes as well as different types of top down nano structures such as holey silicon, honeycomb silicon and others. The methods used is typically Plasma Enhanced Chemical Vapor deposition, Atomic Layer Deposition, Sputtering, and top down procedures including various types of etching. Common for all these methods is that the production rate is very slow and the products are very expensive.
Further relevant art is described in the patent publications US 2015/0368113 A1, WO 2014/060535 A1, US 2010/0266902 A1 and patent publications in the names of Amprius and Nexeon, respectively.
A demand exists for silicon anode material for rechargeable lithium ion batteries, resulting in better combination of storage capacity, number of charging cycles and cost for lithium ion batteries A demand also exists for silicon based surface modified nano particles with a narrow size distribution for other applications, such as 3D printed electronics and energy storage devices, printed electronics and the like. The objective of the invention is to meet said demands.
The invention provides a method for producing silicon particles for use as anode material in lithium ion rechargeable batteries, distinctive by the steps:
a) optionally, to introduce silicon seed particles and/or lithium seed particles into, or producing silicon or lithium seed particles or inner core material in a rotatable reactor, as a separate optional step or as included in step b),
b) to introduce a silicon-containing first reaction gas for CVD into the reactor, setting the reactor in rotation under CVD-conditions; to grow silicon-rich core particles on the seed particles while the reactor is rotated at a rotational speed creating a centripetal acceleration exceeding at least 1000 times the natural acceleration of gravity on said core particles,
c) optionally, to introduce a second reaction gas, liquid or material into the reactor of steps a) and b) or a second reactor into which the core particles of step b) have been introduced; to grow a second material of lower silicon contents than the core material, and the second reaction gas, liquid or material is different from the first reaction gas.
In many preferable embodiments, the method comprises the further step:
d) to introduce a third reaction gas, liquid or material into the reactor of steps a)-c) or a second or third reactor into which the particles of step c) have been introduced; to grow a third material of lower silicon contents than the second material on the particles of step c), the third reaction gas, liquid or material is different from the second reaction gas, liquid or material.
Preferably, one, or both of steps c) and d) takes place under CVD-conditions while the reactor rotates.
Preferably, the rotation in step b) is creating a centripetal acceleration exceeding at least 2000 times g, where g is the natural acceleration of gravity, on said core particles, more preferably exceeding at least 3000 g, 4000 g or 5000 g, more preferably at least 10 000 g, even more preferably at least 25 000 g or 50 000 g or 100 000 g.
Preferably, the method steps are performed under inert conditions, meaning that the resulting particles are not subject to unintentional reactions by oxygen or other gases or materials. This is preferably achieved by using the reaction gas or material for each step if particles are to be introduced from one reactor to another, or retaining the reaction gas or material, or using an inert gas such as nitrogen, for shielding and/or as transport medium.
For some embodiments, it is preferable to have the particle surfaces saturated with hydrogen, dependent on subsequent steps. To retain the surface hydrogen, it is preferable to lower the temperature to below 300° C. and keep the particles in a hydrogen atmosphere. If it is not preferable to retain hydrogen on the particle surface, it is preferable to increase the temperature to above 700° C. in nitrogen or for example argon, to increase the hydrogen desorption rate.
If only the silicon-rich core particles are produced, said core particles are preferably stored and transported in an inert medium to avoid destructive passivation or degradation thereof. Also with the optional second material, and also with the optional third material, the particles are preferably stored and transported in an inert medium to avoid destructive passivation or degradation thereof, thereby increasing shelf life and service life. Preferably, the method and the particles includes at least the step for growing the second material and the second material, respectively, providing particles that can be supplied directly to the battery producer.
Preferably, the method of the invention comprises the step to introduce lithium seed particles into, or producing lithium seed particles or lithium inner core material in a rotatable reactor. The lithium inner core material can be distinct lithium inner core particles or of gradually decreasing lithium concentration from an inner core of highest lithium concentration. The reasoning for this preferable feature of the method of the invention, is that the first time the lithium goes out of the silicon particles of the invention void structures are thereby formed, which void structures will prevent cracking at later recharging cycles.
The second material and when present, the third material, protect the produced particles from degradation, increasing the service life, such as number of charging-recharging cycles, and shelf life of the produced particles.
Preferably, the first reaction gas comprises one or more of SiH4, Si2H6, SiHCl3 and higher order silanes and chlorosilanes, and any combinations thereof.
Preferably, the second reaction gas, liquid or material comprises C, O or N in combination with silicon, such as SiOx, SiCx, SiNx; amorphous carbon, graphite, low-crystalline carbon or low range order graphene structures; C, O and N containing materials combined or replaced with a metal capable of alloying with lithium, for example Ge, GeOx, In, Bi, Mg, Ag, Zn, ZnOx, FeOx, SnOx and TiOx or alloys or composite alloys combining several metals in a structured geometrical pattern and/or in radially distributed layers outside the silicon core particle, alone or in any combination.
For SiOx reaction gas, x can have any naturally occurring value. However, preferably x is in the range [0.5-1], that is from and including 0.5 to and including 1.
The transition between steps b) and c) is discrete or gradual, or any transition in between. Preferably, said transition is in substance linear to the inverse mean diameter or radius of the particles grown, and the transition between steps c) and d) is discrete or gradual, or any transition in between, preferably in substance linear to the inverse mean diameter or radius of the particles grown.
In a preferable embodiment, the second and/or third reaction gas, liquid or material of step d) comprises lithium. The resulting particles, comprising lithium, may provide increased battery service life by avoiding premature reaction with the electrolyte.
The invention also provides use of at least one rotatable reactor for the method of the invention for producing silicon particles for use as anode material in lithium ion rechargeable batteries.
The present invention also provides silicon particles for use as anode material in lithium ion rechargeable batteries, distinctive in that the particles comprises
Preferably, the silicon rich core particles have a purity above 99% by weight of silicon, more preferably at least a purity of 99.5% by weight of silicon.
Preferably, lowering of silicon contents is discrete or gradual, or any transition in between. Preferably, said lowering is in substance linear to the inverse mean diameter or radius of the particles, in direction radial from the core through the second material and further through the third material if present.
The mean diameter range of the in substance spherical silicon core, is 5-750 nm, more preferably 40-200 nm, 10-150 nm, 30-270 nm, 10-90 nm, 20-200 nm, 50-750 nm, 10-150 nm, 50-670 nm, 10-250 nm, more preferably 5-50 nm, with upper and lower limits freely chosen from and within the ranges above. The mean core diameter is preferably below 100 nm, such as about 92 nm. The core particle sizes are measured by standardized methods; preferably laser diffraction according to ISO 13320 (2009), more details are found at the link: http://www.malvern.com/en/products/technology/laser-diffraction/
The overall silicon particle size, including the second layer and optionally the third layer, has D50 and mean diameter preferably about 1-100 nm larger, more preferably 1-50 nm larger, than the silicon rich core particles. The standard deviation of overall particle size mean diameter preferably is identical or similar to as for the core particles.
In the context of the present invention, the term diameter refers to the diameter of a spherical particle or the longest length or dimension in a more or less sphere-shaped particle.
In the context of the present invention, core particles are termed silicon core particles, primary particles, first particles and other terms, understandable from the text.
As well known in the art, D50 means that 50% of the particles are smaller and 50% of the particles are larger than the D50 mean size.
For a D50 of for example 100 nm, the standard deviation shall be less than 50 nm.
For silicon particles of the invention, be it silicon core particles or particles with silicon core and second material or particles with silicon core, second material and third material, the standard deviation is less than 50% of the absolute value of D50. For said particles, said standard deviation preferably is less than 40%, more preferably less than 30%, even more preferably less than 25%, 20% or 15%.
The term precursor may term the reaction gas or reaction material of steps a), b), c) or d), pure or mixed as explained, as understandable from the text.
Preferably, the particles of the invention comprises a lithium inner core material, introduced as seed particles or produced in the rotatable reactor. The lithium inner core material can be distinct lithium inner core particles or of gradually decreasing lithium concentration from an inner core of highest lithium concentration. The reasoning for this preferable feature of the particles of the invention, is that the first time the lithium goes out of the silicon particles of the invention void structures are thereby formed, which void structures will prevent cracking at later recharging cycles.
Preferably, the particles are produced by the method of the invention.
The particles are of a smaller core size and narrower core size distribution and/or finished silicon particle size distribution, either for a specific cost than comparable particles produced by other methods or the particles are novel per se.
The silicon particles of the invention may be part of structures, which structures comprising silicon particles of the invention are embodiments of the present invention. Said structures can be anodes for rechargeable lithium ion batteries, modules or elements for anodes for lithium ion rechargeable batteries or the finished lithium ion batteries. In addition, said structures can be 3D printed structures, printed electronic circuits and other battery types for which surface-modified monodisperse particles of the invention are beneficial.
The invention also provides a reactor for operating the method of the invention, comprising a reactor chamber, an inlet and an outlet or a combined inlet and outlet, and means to heat the reactor chamber to at least 580° C., distinctive in comprising a motor arranged to rotate the reactor at rpm to provide at least a centripetal acceleration of 1000 g on the produced silicon particles, where g is the natural acceleration of gravity, and the inlets and outlet are rotatable at said rpm without leakage at pressure to above 1 bar and temperature of at least 580° C.
The reactor is designed to specifically tailor the growth of the particles by the fluid mechanical and thermal field as well as the chemical composition of the incoming gases. This tailored growth regime results in a narrow distribution in size and geometry. The second stage of the growth is preferably to introduce a second gas, liquid or solid matter in order to produce a composite structure or structure consisting of composite particles to obtain a complete active anode material ready to be adhered to a conductive metallic foil and installed into a battery. The first stage of the particle growth, step b) growing the silicon core, takes place in a reactor where the layout of the reactor is in the form of a centrifuge in order to be able to introduce large centripetal forces without having large velocity gradients at the wall. The result is a controlled high centripetal force field without too high turbulence intensity, providing narrower size and geometry distribution of the grown particles, which is discussed below.
Reference is made to
Upon the primary silicon rich core particles a second material (2) comprising carbon in the form of graphite, graphene, amorphous carbon, including but not restricted to low range order crystalline carbon including but not restricted to carbon deposited from a gaseous precursor such as acetylene or methane. The second material may comprise SiOx, SiCx, SiNxincluding but not limited to SiC, SiO2 and α-Si3N4 in combination or not with a metal capable of alloying with silicon including but not limited to Ge, GeOx, Mg, Ag, Zn, ZnOx, Fe, FeOx, SnOx, TiOx, Ni, In, B, Sn, Ti, Al, Ni, Sb and Bi including but not limited to NiSi, CaSi2, Mg2Si, FeSi, FeSi2, CoSi2, Al2O3, TiO2, CO3O4, B4C and NiSi2, alone or in any combination. The second material (2) may comprise carbon in the form of graphene deposited from acetyelene or methane onto a hydrogensaturated silicon surface. The graphene may or may not be n-doped by phosphorous or nitrogen or p-doped by beryllium, boron, aluminum, or gallium depending on the layout and composition of the anode. The second material (2) may comprise SiC that may be n-doped by phosphorous or nitrogen or p-doped by beryllium, boron, aluminum, or gallium depending on the desired layout and composition of the anode. Preferably n-doped with the current state of the art anode and battery layouts. The second material may be formed by decomposing a carbon containing decomposable precursor including but not limited to acetylene, methane or propane together with a silicon containing precursor including but not limited to SiH4 or Si2H6 and subsequently subject the surface to a decomposable precursor containing the dopant and heat the dopant containing precursor until decomposition. Such a precursor may comprise PH3, NH3 or B2H6, as well as other decomposable precursors. If deposition of the second material is performed in a second chamber this chamber may have a substantially different operation conditions from the first chamber including but not limited to higher temperature, lower pressure and/or have radio-frequency plasma-enhanced deposition (PECVD), microwave PECVD or electron-cyclotron resonance PECVD in order to chose from a wider selection of possible dopant containing precursors decomposable within the operation parameter domain of the reactor.
Reference is made to
In one preferred embodiment the first material (1) is a silicon containing material such as amorphous Si or α-Si3N4, the second material (2) is C primarily in the form of graphene and the third material (3) is porous flexible carbon and silicon containing solid such as C2H6Si produced from reaction of a carbon containing gaseous precursor such as CH4 or C2H2 and a silicon containing precursor such as SiH4 at the outside of the second material (2).
Reference is made to
After the core silicon particles have been formed they may either be further processed in the same chamber or they may be harvested and processed in a second chamber. In an embodiment where the different stages of the particle growth are performed in different reactors the particle harvest from the first reactor may either be from accumulation of particles at the wall (10) or retrieved from the exiting gas flow (12), each of which options represents embodiments of the invention.
Further reference is made to
Reference is made to
Reference is made to
Reference is made to
SiH4 is supplied to a rotational reactor maintaining an artificial gravity field of 10 000 G. The chamber is heated to 580° C. and the gas decomposes and produced silicon particles of 10-150 nm. The primary silicon particles are retrieved from the chamber and fed to a second chamber rotating at 1000 G maintaining a temperature of 640° C. In the second chamber CH4 is supplied together with SiH4 and a second layer of SiC of 0-5 nm thickness is deposited onto the primary particles.
Si2H6 is supplied to a rotational reactor maintaining an artificial gravity field of 8 000 G. The chamber is heated to 650° C. and the gas decomposes and produced silicon particles of 30-270 nm. The primary silicon particles are retrieved from the chamber and fed to a second non rotating chamber at 30° C. with 0.5% O2 in H2 and a layer of SiOx is formed at the surface of the particles of 1 to 5 nm thickness. The particles are then harvested and fed into a third non rotating chamber holding 680° C. In the third chamber CH4 is supplied and a third layer of crystalline carbon of 0-5 nm thickness is deposited onto the particles.
SiH4 is supplied to a rotational reactor maintaining an artificial gravity field of 10 000 G. The chamber is heated to 690° C. and the gas decomposes and produced silicon particles of 10-90 nm. The primary silicon particles are retrieved from the chamber and fed to a second chamber rotating at 1000 G maintaining a temperature of 720° C. In the second chamber CH4 is supplied and a second layer of crystalline carbon of 5-15 nm thickness is deposited onto the primary particles.
50 atm % SiH4 in 50 atm % H2 is supplied to a rotational reactor maintaining an artificial gravity field of 10 000 G. The chamber is heated to 550° C. and the gas decomposes and produced silicon particles of 20-200 nm. The primary silicon particles are retrieved from the chamber and fed to a second non rotating chamber at a temperature of 530° C. In the second chamber 10 atm % CH4 is supplied together with 10 atm % SiH4 and 80 atm % H2 and a layer of vinylsilane C2H6Si of a thickness of 1-10 nm is deposited onto the particles.
SiH4 is supplied to a rotational reactor maintaining an artificial gravity field of 1 000 G. The chamber is heated to 550° C. and the gas decomposes and produced silicon particles of 50-750 nm. The primary silicon particles are retrieved from the chamber and fed to a second non rotating chamber at a temperature of 480° C. In the second chamber titanium isopropoxide, Ti(OPri)4is supplied and a layer og TiOx is deposited onto the particles in a thickness of 0-3 nm. The particles are then retrieved and fed into a third rotating chamber maintaining a temperature of 520° C. and an artificial gravity field of 3000 G. In the third reactor chamber C2H2 is supplied and a layer of crystalline carbon of a thickness of 5-25 nm is deposited onto the particles.
40 atm % SiH4, 30 atm % NH3 and 30 atm % H2 is supplied to a rotational reactor maintaining an artificial gravity field of 10 000 G. The chamber is heated to 620° C. and the gas decomposes and produces α-Si3N4 particles of 10-150 nm. The α-Si3N4 particles are harvested from the chamber and mixed with 1 atm % 2,4′-sulfonyldiphenol and 1 atm % Ni particles of a particle size of 1-8 nm dispersed in a liquid solution of 20 atm % tetrahydrofuran and 68 atm % ethanol. The particles are then filtrated out of the solution and dried in 60° C. N2 for 2 hrs. The core particles with deposited carbon and Ni particles is then heat treated in a fluidized bed chamber with N2 at 720° C. for 3 hours and harvested. The carbon and Ni coating layer will be of 5-20 nm thickness depending on several factors including the mixing process and the fluid mechanical properties within the FBR. If the fluidization intensity is too high some of the carbon will peel off and become independent carbon particles.
Concentration of the precursor in the in-feed gas, the temperature of the reactor chamber, the pressure, residence time within the reactor, concentration of catalytic gases, liquids or solids as well as the spatial gradients of these values will all influence the growth and hence the particle size distribution. However, by utilizing rotational velocity to control the size distribution it is possible to maintain a favorable size distribution even at high production rates and low power consumption.
Given 80 atm % SiH4 in 20 atm % H2 in the feed gas into a reactor temperature of 650° C., 1 bar pressure, at an average reactor residence time of 4 seconds the influence of rotational velocity on particle size distribution is substantial. The table is based on a non-catalytic reactor chamber. If the reactor chamber is catalytic to the chemical process the particle onset temperature will be lower and shift the particle size distribution to lower sizes.
A reactor of 100 mm diameter reactor rotating at 13 400 rpm will have a centripetal acceleration of about 10 000 G and under the conditions given in this example have a particle size distribution of 10-250 nm. The centripetal acceleration can be calculated from the square of the velocity, in m/s, divided on the reactor radius, in meter.
With the rotating reactor and method of the invention, the combination of high production rate, narrow size distribution, small sized particles and in substance spherical particles, are provided, which results in lower cost. The rotation allows higher gas pressures or precursor concentrations whilst avoiding unwanted side-reactions and effects, compared to other methods and reactors. The method of the invention may comprise any step or feature as here described or illustrated, in any operative combination, each such combination is an embodiment of the invention. The reactor of the invention may comprise any step or feature as here described or illustrated, in any operative combination, each such combination is an embodiment of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20161490 | Sep 2016 | NO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NO2017/050235 | 9/19/2017 | WO | 00 |
