KR102093588B1 - Positively charged silicon for lithium-ion batteries - Google Patents

Abstract

The present invention relates to a negative electrode material for a lithium-ion battery comprising silicon and having a chemically treated or coated surface that affects the zeta potential of the surface. The active material consists of particles or particles and wires comprising a core 11 comprising silicon, wherein the particles have a positive zeta potential in a section between pH 3.5 and 9.5, preferably between pH 4 and 9.5. Have The core is chemically treated with an amino functional metal oxide, or the core is an O _y SiH _x group, where x is greater than 1 and less than 3, y is greater than 1 and less than 3, and x is greater than y. At least partially covered, or the core is covered with adsorbed inorganic nanoparticles or cationic polyvalent metal ions or oxides.

Description

Positively charged silicon for lithium-ion batteries {POSITIVELY CHARGED SILICON FOR LITHIUM-ION BATTERIES}

The present invention relates to a negative electrode material for a lithium-ion battery comprising silicon and having a chemically treated or coated surface that affects the zeta potential of the surface.

Li-ion technology dominates the portable battery market and is a strong candidate for EV and HEV applications. Thus, for such large volume applications, in addition to the need for higher energy density and power rate electrodes, safety and cost issues must be overcome. To solve this problem, a wide variety of research directions have been successfully investigated to some extent, requiring different Li-reactive mechanisms (conversion, substitution and alloying reactions) compared to classical Li insertion mechanisms. Clearly due to recent discoveries, nanomaterials are in the stage of rapid implementation in commercial cells both on the positive side with an intercalation compound (olivine LiFeP0 ₄ ) and on the negative side with an alloying reaction.

An experimental study on the electrochemical alloying of elements using lithium was when Day described the formation of Li alloys using Sn, Pb, Al, Au, etc. at room temperature and pointed out that they were similar to those produced by metallurgical methods. It started in the early 1970s. In 1976, Li was found to react electrochemically with Si at high temperatures through continuous formation of Li ₁₂ Si ₇ , Li ₁₄ Si ₆ , Li ₁₃ Si ₄ and Li ₂₂ Si ₅ phases. We know that this electrochemical reaction is limited to the Li ₁₅ Si ₄ monocomponent at room temperature, but regardless of their properties (intercalation, alloying, conversion), the corresponding gravity (3579 mAh / g) and volume ( The 8330 mAh / cm ³ ) capacity far ahead of all other Li absorption reactions identified so far, and self-justify the past, present and certainly future focus on this system.

Thus, the imperfections inherent in the alloy-based electrode are caused by the large volume swing during subsequent charge / discharge, which results in the electrochemical grinding of the electrode and its resulting electrical exudation loss, and enormous electrolyte decomposition on the particle surface in the process. Have been at their poor cycling life (eg, rapid capacity loss). To avoid this problem, the first solution was to use electrodes made of nanoparticles, because the conventional mechanism of deformation and displacement is not the same as on a microscale, ie because small particles can release stress without breaking. Unfortunately, these nanoscale silicon powders oxidize rapidly when exposed to air, and the surface of Si made in situ in a commercially available Si or plasma process as disclosed in International Patent Application Publication No. WO2012-000858 (protonated Silanol groups are covered by SiOH. These surface silanol groups cause non-optimal behavior of silicon particles at the cathode during the life of the battery.

Other methods of maintaining electrode integrity are 1) manufacturing a metal thin film that provides the best electrical contact through strong adhesion to the substrate to enable high quality electrical contact during cycling, 2) Si / C / carboxy with interesting cycling properties Preparation of a (metal-carbon-binder) composite electrode with an appropriate binder so that a -methyl-cellulose (CMC) electrode is achieved, or 3) metal-carbon (Si / C, with Si / C, acting as a volume buffer matrix) Sn / C) It is refined through thermal decomposition of the organic precursor of the composite.

Significant progress has been made over the past decade to improve the behavior of the silicon-based electrode with improved slurry production and the selection of good binders. Nevertheless, the active material particles need to be further adjusted to realize the next step of improvement, especially to provide better capacity retention during cycling. Today, when the negative electrode capacity can be maintained as a lithium counter electrode, a silicon-based metal-based electrode generally provides weak capacity retention with a positive electrode containing a limited amount of lithium. To solve this problem, the silicon surface needs to be modified to limit electrolyte decomposition.

Different methods can be used to modify and protect the silicon surface. However, it is also necessary to select a new surface according to the reactivity of the electrolyte, since the material needs to increase the potential range of stability of the electrolyte to reduce electrolyte decomposition. In US Patent Application Publication No. 2011/0292570, Si nanoparticles having a positive surface charge are coated with graphene. The positive charge is preferably a functional group selected from an amino group and an ammonium group, such as NR ₂ and NR ₃ ⁺ , where R is selected from H, C ₁ -C ₆ -alkyl and C ₁ -C ₆ -hydroxyalkyl. Caused by alteration of the surface of the nanoparticles.

It is an object of the present invention to disclose new Si base particles used in the negative electrode of a rechargeable battery that can provide better capacity retention during cycling.

Viewed from the first aspect, the present invention can provide a negative electrode material for use in a lithium rechargeable battery comprising a core comprising silicon, wherein the material is pH 3.5 to 9.5, preferably pH 4 to It has a positive zeta potential in the interval of 9.5. In some embodiments, the zeta potential is +10 mV or more, preferably +20 mV or more, in a pH section of 3.5 to 9.5, even in a pH section of 4 to 9.5. The advantage of having a higher zeta potential is to improve the dispersion between carbon, active material and binder during paste preparation in aqueous media. Zeta potential naturally refers to the potential measured in demineralized water. The core material may have a nanometer size (thus having one or more dimensions of less than 100 nm), a size of less than a micrometer, or a micrometer size, and may include a mixture of nano-sized Si particles and nano-sized Si wire. In this case, the average particle size of the Si particles is, for example, as described in International Patent Application Publication No. WO2012-000854, at least 5 times the average width of the Si wire, preferably at least 10 times the average width of the Si wire. This negative electrode material for Li-ion secondary batteries offers significant advantages in that it limits capacity loss during cycling. In one embodiment, the material has a zero charge point at pH 4 or higher, preferably at pH 7 or higher.

In another embodiment, the negative electrode material has a specific surface area characterized by a BET value of 1 to 60 m 2 / g, preferably 20 to 60 m 2 / g. In another embodiment, the core has an average particle size of 20 nm to 200 nm (average particle diameter was calculated by assuming the theoretical density of non-porous spherical particles and individual materials). The equation for calculating the nanometer-sized average particle diameter without going through the total differential is 6000 / ((BET surface area in m2 / g units) x (density in g / cm3)),

-Pure silicon (at least metallurgical grade), or

-A silicon monoxide powder composed of a mixture of nanometer-sized Si and SiO ₂ , which can have a micrometer size, or

Silicon having a SiO _x surface layer (where x is greater than 0 and less than 2) having an average thickness of 0.5 nm to 10 nm, or

-The formula SiO _x . (M _a O _b ) _y (where x is greater than 0 and less than 1, y is greater than or equal to 1 and less than 1, a and b are selected to provide electrical neutrality, M is Ca, Mg , A homogeneous mixture of silicon oxide and metal oxide, having one or more of Li, Al and Zr), or

-Alloy Si-X (where X is one or more metals from the group consisting of Sn, Ti, Fe, Ni, Cu, Co and Al)

It consists of. Pure silicon can have a nanometer size. In some embodiments, silicon can be coated with carbon. The silicon material may be a Si powder having an average primary particle size of 20 nm to 200 nm, wherein the powder has an average thickness of 0.5 nm to 10 nm, for example, as disclosed in International Patent Application Publication No. WO2012-000858. SiO _x (where x is greater than 0 and less than 2) has a surface layer. The above-mentioned alloys are metals other than Si, such as Sn, as disclosed in U.S. Patent Application Publication No. 2010-0270497, International Patent Application Publication No. WO2007-120347 or co-pending International Patent Application PCT / EP2011 / 068828. Ti, Ni, Fe, Cu, Co and Al.

In one particular embodiment, the surface of the core has O _y SiH _x (where x is greater than 1 and less than 3, y is greater than or equal to 1, and x is greater than y) groups. It is also conceivable that the O _y SiH _x group is a mixture of silanol (SiOH) and SiH _x (where x is greater than 1 and less than 3). The presence of silanol groups and SiH _x can be detected by the following methods:

¹ H MAS NMR spectroscopy showing two different regions at about 1.7 ppm and about 4 ppm. The first region corresponds to Si-OH, while the second region is assigned to adsorbed water or SiH _x groups.

²⁹ Si MAS / CPMG NMR spectroscopy showing at -100 ppm a first band that can be attributed to an isolated silanol or adjacent silanol for two silicons, a silicon atom bearing a single hydroxyl group. Another band present at -82 ppm is assigned to silicon (SiH _x ) with at least one hydrogen.

-DRIFT infrared spectroscopy showing the presence of various crystal modes as well as Si-O-Si mode at about 1100 cm ^-1 . The peaks of about 3500 cm ^-1 are due to hydroxylated silanol groups. 2260 cm ^- different peak between ¹ and 2110 cm ^-1 it can be assigned to the SiH _x O _y transform mode.

In another embodiment, the surface of the core is at least partially covered by a coating composed of inorganic nanoparticles. The fact that the surface is at least partially covered here further adds a group of cores having an O _y SiH _x (where x is greater than 1 and less than 3, y is greater than or equal to 1, and x is greater than y). It means you can hold it. These inorganic nanoparticles may be one of aluminum compounds (eg, Al ₂ 0 ₃ ), zinc compounds (eg, zinc oxide) and antimony compounds (eg, antimony oxide). In one embodiment, the nanoparticles in the coating consist of a precursor material that is prone to conversion to one of aluminum, zinc and antimony by reduction. The nanoparticles can form a first coating layer having a thickness of less than 10 nm on the core. The first coating layer preferably has a thickness between 1 nm and 5 nm. As a second coating layer positioned between the core of the nanoparticles and the first coating layer, a second coating layer including carbon or aluminum may be provided. One or both of the first coating layer and the second coating layer may exhibit electrochemical activity. In embodiments where the surface of the core is at least partially covered by a coating composed of inorganic nanoparticles, the surface of the core is O _y SiH _x (where x is more than 1 and less than 3, y is 1 or more and 3 or less, x May be greater than y).

In another specific embodiment, the surface of the core is at least partially covered by an adsorbed cationic polymer having one or more of primary amine functionality, secondary amine functionality and tertiary amine functionality. The fact that the surface is at least partially covered here further adds a group of cores having an O _y SiH _x (where x is greater than 1 and less than 3, y is greater than or equal to 1, and x is greater than y). It means you can hold it. In another specific embodiment, the surface of the core is at least partially covered by adsorbed cationic polyvalent metal ions. The fact that the surface is at least partially covered here further adds a group of cores having an O _y SiH _x (where x is greater than 1 and less than 3, y is greater than or equal to 1, and x is greater than y). It means you can hold it. In one embodiment, the metal ion can be one or more of the group consisting of Al-ion, Sb-ion, Fe-ion, Ti-ion and Zn-ion. This embodiment can be combined with embodiments in which the surface of the core has O _y SiH _x (where x is greater than 1 and less than 3, y is greater than or equal to 1, and x is greater than y) groups. . In a further specific embodiment, the surface of the core is at least partially covered by adsorbed nanoparticles of cationic polyvalent metal oxide. The fact that the surface is at least partially covered here further adds a group of cores having an O _y SiH _x (where x is greater than 1 and less than 3, y is greater than or equal to 1, and x is greater than y). It means you can hold it. In one embodiment, the metal oxide is at least one of the group consisting of Al-oxide, Ca-oxide, Mg-oxide, Pb-oxide, Sb-oxide, Fe-oxide, Ti-oxide, Zn-oxide and In-hydroxide. to be. In another further specific embodiment, the surface of the core is at least partially covered by a silanol group (-Si-0 ^- group) covalently bonded to an amino-functional metal compound, wherein the metal is Si , Al and Ti. The fact that the surface is at least partially covered here further adds a group of cores having an O _y SiH _x (where x is greater than 1 and less than 3, y is greater than or equal to 1, and x is greater than y). It means you can hold it. In one embodiment, the amino functional metal compound used to chemically treat the core surface can be an alkoxide.

Viewed from the second aspect, the present invention can provide the use of the above-described active substance in the negative electrode further comprising a water-soluble or N-methylpyrrolidone soluble binder material. The negative electrode may further include graphite.

Viewed from the third aspect, the present invention can provide a method of manufacturing a cathode material, comprising the following steps:

-Providing a nanometer-sized silicon material,

-Dispersing the silicon material in water,

-Providing a predetermined amount of cationic polyvalent metal ion to the dispersion,

-Adjusting the pH of the dispersion to a value of 2 to 3.5, preferably 2 to 2.5, and thereafter,

-Adjusting the pH of the dispersion to a value of pH 3.5 to 4,

-Measuring the zeta potential of the dispersion, and if the zeta potential is negative,

-Further adjusting the pH of the dispersion to a value higher than the previous pH value and measuring the zeta potential of the solution, and

-Repeating said adjusting step until a positive zeta potential is measured. When the cationic polyvalent ion is mixed into the dispersion, the silicon material is partially covered by the adsorbed cationic polyvalent metal ion, which is converted to a coating composed of inorganic nanoparticles during a subsequent pH adjustment step. Nanometer-sized silicon materials can be dispersed in demineralized water at neutral pH. The step of adjusting the pH of the dispersion to a value of 2 to 3.5 can be performed by adding HCl. If the pH is adjusted to a value less than 2, there is a risk of dissolving Si in an acid solution. Both the step of adjusting the pH of the dispersion to a value of 3.5 to 4, and, if applicable, further adjusting the pH of the dispersion to a value higher than the previous pH value of 0.5 can be performed by the addition of NaOH. Cationic polyvalent metal ions can be present in nanometer-sized silicon materials as (accidental) dopants or can be added to the water used to prepare the dispersion.

The present invention can also provide a method of making a cathode material comprising the following steps:

-Providing a nanometer-sized silicon material, and

Under vacuum of at least 1 mbar and 50 ° C. using a gaseous organo-aluminum, organo-zinc or organo-antimony stream and water vapor in the reaction chamber until a layer with a thickness of 2 nm to 10 nm is formed Performing an atomic layer deposition process on the silicon material at a temperature of between -500 ° C. The vacuum may be 10 ^-1 mbar or more, and the temperature may be 150 ° C to 250 ° C to make the process more economical.

The present invention can also provide process embodiments for making a cathode material, comprising the following steps:

-Providing a nanometer-sized silicon material and dispersing the silicon material in water,

-Providing a predetermined amount of cationic polyvalent metal ion to the dispersion,

-Mixing the dispersion to at least partially cover the silicon material with adsorbed cationic polyvalent metal ions, and

-Drying the metal ion-silicon mixture. Nanometer-sized silicon materials can be dispersed in demineralized water at neutral pH. The metal ion may be, for example, one or more of the group consisting of Al-ion, Sb-ion, Fe-ion, Ti-ion and Zn-ion. The drying step may include heating at 70 ° C. to 100 ° C. under vacuum for at least 1 hour. This process can include an additional step of redispersing the dry metal ion-silicon mixture in water, and an additional step of acidifying the dispersion to a pH of 2-6. In this way a higher value for zeta potential is achieved. The two additional steps can be combined by redispersing in an acid solution at a pH of 2-6. This method embodiment may be combined with the first named process in the third aspect of the invention.

The present invention can also provide a method of making a cathode material comprising the following steps:

-Providing a nanometer-sized silicon material,

-Dispersing the silicon material in water containing ammonium ions, and covering the surface of the silicon material with silanol groups,

-Providing an amino functional metal oxide compound to the mixture,

-Stirring the mixture to covalently bond the silanol group to the amino functional metal compound, and

-Drying the mixture. Ammonium ions are added to adjust the pH of the solution. The solution may include ethanol to further facilitate dissolution of the metal oxide compound. The drying step may include heating at 70 ° C. to 100 ° C. under vacuum for at least 1 hour. Before this step, a washing step using ethanol may be performed. The metal in the metal oxide compound may be, for example, one or more of the group consisting of Si, Al and Ti.

The present invention can also provide a method of making a cathode material, comprising the following steps:

-Providing a nanometer-sized silicon material,

-Dispersing the silicon material in water,

-Adding a predetermined amount of cationic polyvalent metal oxide nanoparticles to the dispersion,

-Stirring the dispersion to at least partially cover the surface of the silicon material with adsorbed nanoparticles of cationic polyvalent metal oxide, and

 -Drying the metal oxide-silicon mixture. Nanometer-sized silicon materials can be dispersed in demineralized water at neutral pH. The metal oxide may be, for example, one or more of the group consisting of Al-oxide, Ca-oxide, Mg-oxide, Pb-oxide, Sb-oxide, Fe-oxide, Ti-oxide, Zn-oxide and In-hydroxide. . The drying step may include heating at a temperature of 70 ° C to 100 ° C under vacuum for at least 1 hour.

In different process embodiments, the final product can have an open pore volume of less than 0.01 cc / g. In one process embodiment, the nanometer-sized material in each of the above processes may consist of particles or a mixture of particles and wires, wherein both the particles and the wires have nanometer sizes, and the average particle size of the particles Is 5 times or more of the average width of the wire, preferably 10 times or more of the average width of the wire. In another process embodiment, the silicon material

-Pure silicon,

-Silicon monoxide powder composed of a mixture of nanometer-sized Si and Si0 ₂ , which can have a micrometer-sized silicon monoxide powder,

SiO _x surface layer (where x is greater than 0 and less than 2), silicon having a surface layer having an average thickness of 0.5 nm to 10 nm,

-The formula SiO _x . (M _a O _b ) _y (where x is greater than 0 and less than 1, y is greater than or equal to 1 and less than 1, a and b are selected to provide electrical neutrality, M is Ca, Mg , Li, Al and Zr), a uniform mixture of silicon oxide and metal oxide, or

-Alloy Si-X (where X is one or more metals from the group consisting of Sn, Ti, Fe, Ni, Cu, Co and Al)

It can be composed of.

Viewed from the fourth aspect, the present invention can provide a method of manufacturing an electrode assembly for a rechargeable Li-ion battery comprising the negative electrode material described above, comprising the following steps:

-Dispersing the negative electrode material in an aqueous solution to obtain a first slurry,

-Adjusting the pH of the first slurry to a value within a section where the zeta potential of the material is positive,

-Dissolving the CMC salt in water to obtain an aqueous solution of the binder material,

-Adjusting the pH of the aqueous solution of the binder material to a value within a section in which the zeta potential of the material is positive, preferably the pH value of the first slurry,

-Mixing the first slurry with an aqueous solution of the binder material to obtain a second slurry,

-Dispersing the conductive carbon in the second slurry,

-Spreading the second slurry onto a current collector, preferably a copper foil, and

Curing the electrode assembly comprising the second slurry at a temperature of 105 ° C to 175 ° C.

1: Schematic diagram of silicon particles 21 having a positively charged layer 22 surrounded by a negatively charged polymer 23.
Figure 2: Schematic diagram of silicon particles (or primary particles) 11 having the following A-D: A: Coating 12 with inorganic layer; B: physically adsorbed organic molecule 13; C: chemically attached organic molecule 14; And D: nanoparticles (secondary particles) 15 adsorbed on the surface of the primary particles.
Figure 3: Schematic diagram of ALD reactor with P for pump, Np for nanopowder and Ar for argon gas source.
4: TEM photograph of silicon particles 61 with alumina coating 62.
Figure 5: Comparison of the zeta potential (mV) of the coated silicon (1) to pH and intact silicon (2).
Figure 6: Viscosity increase over time for silicon and coated silicon suspension in CMC solution, □ = CMC alone (blank test), ● = intact silicon (reference), Δ = alumina coated silicon.
Figure 7: Comparison of the reversible delithification capacity (1) of a battery using coated silicon as the negative electrode material and the delithization capacity (2) of a battery using natural silicon as the negative electrode material.
Figure 8: Reversible delithification capacity of a battery using alumina coated silicon (25 cycles of ALD) as the negative electrode material.
Figure 9: TEM photo of silicon nanowires with alumina coating. EFTEM map of samples using alumina contrast (b), silicon contrast (c) and oxygen contrast (d).
10: Comparison of zeta potential (mV) and intact nanowires according to pH of nanowires (coated nanowires) 1 (2).
Figure 11: Zeta potential (mV) according to pH of acid-base treated silicon.
Fig. 12: Comparison of the reversible delithification capacity (1) of a battery using treated silicon as a negative electrode material and the delithification capacity (2) of a battery using natural silicon as a negative electrode material.
Figure 13: Comparison of zeta potential (mV) versus pH (1) of APTS (Si: APTS = 4/5) coated silicon and intact silicon (2).
Figure 14: Comparison of zeta potential (mV) vs. pH (1) of silicon with adsorbed alumina nanoparticles and intact silicon (2).
Figure 15: Reversible delithification capacity (mAh / g vs. number of cycles) (1) of a battery using alumina adsorbed silicon as the negative electrode material and reversible delithium of a battery using alumina-treated silica adsorbed silicon as the negative electrode material Shoes capacity (2).
Figure 16: Comparison of zeta potential (mV) vs. pH (1) of silicon with physically adsorbed cationic polymer and intact silicon (2).
Figure 17: Zeta potential of cationic coated silicon (mV) versus pH (1) and comparison with intact silicon (2).
Figure 18: Reversible de-lithiation capacity (mAh / g versus number of cycles) of a battery using cationic coated silicon as the negative electrode material.
Figure 19: Zeta potential (mV) versus pH (different BET) of alumina coated silicon and comparison with intact silicon (same initial BET) (2).
Figure 20: Zeta potential (mV) of alumina coated silicon monoxide vs. pH (1) and comparison with intact silicon monoxide (2).

The object of the present invention is to propose a modified particle surface for Si-containing particles to maintain capacity throughout the cycle and reduce the reactivity of the electrolyte and the surface with good interaction with the binder. The method proposed in the present invention is to alter the particle surface, and to produce a positively charged surface that is a surface with a positive zeta potential within a portion of the pH range of 3.5 to 9.5.

Positively charged particles are characterized by dispersing 20 g / L of powder in distilled water. The zeta potential 'Z' of the dispersion in an aqueous medium is measured, for example, using a Zetaprobe Analyser ™ from Colloidal Dynamics. Finally, when Z is higher than 0, the particle is defined as being a positively charged particle at a certain pH, and a negatively charged particle is defined as a particle having Z less than 0. This is illustrated in FIG. 1.

The silicon surface is naturally negatively charged at neutral pH, and can be positive at pH 2 to 3 (silica isoelectric point or IEP). Chemical surface groups are primarily deprotonated silanol groups. This charge does not favor good interaction with the negatively charged binder. Indeed, preferred binders are water-soluble polymers that are negatively charged at neutral or even lower pH, such as carboxymethylcellulose binder (CMC) or polyacrylate PAA.

We propose four different ways to modify the particle surface (see Figure 2):

(A) A method using at least partial coating of an inorganic layer (for example, coating of alumina, zinc oxide or antimony oxide) by a layer deposition method (whereby the particles include a core comprising silicon and an inorganic attached to the core) Consisting of layers, wherein the coating is obtained by chemical treatment consisting of sequential acid-base treatment of powders containing the elements of the coating in the future);

(B) a method using physical adsorption of cations (eg, cationic polyvalent metal ions) or organic molecules to the core of particles (eg, cationic molecules);

(C) a method using chemical adsorption (creation of covalent bonds) of organic molecules (eg, grafting of silane type molecules (or generally any amino functional metal oxide) on surface silanol); And

(D) A method using adsorption of nanoparticles (secondary particles) to the core of the particles (for example, adsorption of alumina nanoparticles on the silicon surface).

Although FIG. 2 shows spherical particles, the particles may be composed of a wire containing silicon.

When the coating is applied, the coating may be an insulating coating because lithium can diffuse through a thin layer (organic or inorganic layer). In addition, when a thin metal oxide coating is applied, there is an additional advantage that the oxide can be converted to metal oxide and lithium oxide during the first cycle in a lithium-ion battery. This irreversible conversion will create a metallic surface that can produce an alloy with lithium as silicon and generate extra capacity while allowing volumetric expansion; The proposed alumina / aluminum, zinc or antimony coating can grow with volumetric expansion of silicon and continuously protect electrolyte / silicon contact.

Silicon or silicon containing materials charged in this amount is tested as a negative electrode in a lithium-ion battery. The powder is mixed with a binder and a carbon conductor to produce a slurry coated on copper foil. The present invention makes it possible to improve the electrochemical behavior of silicon-containing particles by improving the dispersion of silicon, carbon and polymers in coatings on copper foil, improving capacity retention and lowering irreversible.

Example 1: Alumina coated silicon

In this example, an alumina coating is applied by atomic layer deposition (ALD), a deposition method for producing nanometer-sized coatings. In the ALD process, two (or more) alternating surface self-defining chemical vapor deposition reactions are performed. This technique is also used to coat nanopowders. A small amount of powder can be coated using a stationary phase system, but for larger amounts fluidized particle bed reactors or rotary reactors can be used, as illustrated in US Patent Application Publication No. 2011/0200822. A coating of Al ₂ O ₃ can be deposited with thermal ALD using trimethyl aluminum (TMA) and H ₂ O as reactants. The reaction temperature is about 200 ° C. The saturation of the reactive surface can be monitored using mass spectrometry for the degradation product of the precursor.

In this example, a sample was prepared according to International Patent Application Publication No. WO2012-000858 and preheated the sample for 1 hour under a flow of argon at 21 m 2 / g with an open pore volume of less than 0.001 cc / g under argon flow at 150 ° C. Then measured by the ASAP apparatus via isothermal adsorption-desorption of N ₂ at 77K), oxygen content of less than 4% by weight, primary particle size defined as 80 nm <D80 <200 nm and (as defined at pH 7 in water) 5 g of the nano-silicon powder with the initial negative zeta potential is weighed and placed in a glass reactor (see Figure 3). The reactor outlet 3 is connected to a vacuum oil pump at 10 ^-2 mbar. Using a swage lock (swagelok) ^® tube and the automated valves of the reactor gas inlet (1), trimethyl aluminum (TMA) feeder (97%, Sigma-Aldrich) is connected to. The reactor gas inlet 2 is connected to a glass bottle of (deionized) H ₂ O using a Swagelok ^® tube and an automated valve. During one "cycle" the gas flow and water from the TMA are used. Open the valve connecting the reactor to the TMA until the surface is saturated and closed with TMA (5 minutes). After doing this, the valve connecting the reactor to H ₂ O is opened for 5 minutes. Six cycles (TMA followed by water) are used for the preparation of the coating. Equal amounts of intact nano-silicon powder are used as reference examples.

Microscopic observation pictures show a homogeneous and thin (3 nm) conformal alumina coating on the surface of the silicon particles (see Figure 4). The BET surface area of this powder was preheated at 150 ° C. under a flow of argon for 1 hour and then with a void volume of less than 0.001 cc / g from the result of isothermal adsorption-desorption of N ₂ at 77K (21 m 2 for natural silicon) 20 g / m). The amount of aluminum is measured by ICP and a value of 2% by weight is calculated.

Therefore, the ALD process includes the following steps until a coating with a thickness of 2 nm to 10 nm is formed:

-Supplying a nanometer-sized silicon material to the reaction chamber at a temperature of 150 ° C to 250 ° C under a vacuum of 10 ^-1 mbar or more,

-Injecting a gaseous organo-aluminum, organo-zinc or organo-antimony compound into the reaction chamber,

-After saturating the surface of the silicon material with an organo-aluminum, organo-zinc or organo-antimony compound,

-Water vapor is injected into the reaction chamber,

-Providing a coating of aluminum oxide, zinc oxide or antimony oxide to the surface of the silicon material,

-Repeating the step of injecting a gaseous organo-aluminum, organo-zinc or organo-antimony compound into the reaction chamber,

-After saturating the surface of the silicon material with an organo-aluminum, organo-zinc or organo-antimony compound,

-Injecting water vapor into the reaction chamber.

The zeta potential of the generated material is measured according to the following procedure: Both a reference 2% by weight nano-silicon powder and alumina coated silicon suspension in 150 ml of demineralized water are prepared by sonication (120 seconds at 225 W). The zeta potential of this suspension in an aqueous medium is measured with the Zeta Probe Analyzer ™ of Colloidal Dynamics. The sample is automatically titrated from neutral pH to acidic pH with 0.5 M HCl and automatically titrated to a higher basic pH with 0.5 M NaOH.

The high negative surface charge on the nano-silicon powder can be clearly measured (see line 2 in Figure 5). Zeta potential is negative from pH 5 to 2. In the case of alumina coated silicon, the powder has a positive zeta potential from pH 9.5 to at least pH 2.5 (line 1 in FIG. 5).

A slurry is prepared using 50% by weight of this powder (based on the dry residue), 25% by weight of Na-CMC binder (molecular weight <200000) and 25% by weight of conductive additives (Super C65, Timcal). . In the first step, a 2.4% Na-CMC solution is prepared and dissolved overnight. Then, conductive carbon is added to this solution and stirred for 20 minutes using a high-shear mixer. Once a good dispersion of conductive carbon is obtained, the active material is added and the slurry is stirred again for 30 minutes using a high-shear mixer. One of the evidences that the coating hinders the contact between the electrolyte and the silicon surface is an increase in the viscosity of the CMC solution. Flowability is measured under shear rate controlled conditions using a Fysica MCR300 flowmeter with a cone-plate measuring geometry at 23 ° C. When the polymer (CMC in this example) is in contact with the intact silicon surface, we observe the drop in viscosity of the CMC / Si solution / suspension. As shown in FIG. 6, the viscosity is maintained when silicon is coated with alumina compared to the blank test using only CMC (□ = CMC alone, ● = intact silicon (reference), Δ = alumina coated silicon), which It is demonstrated that silicon is completely covered with another material (here, Al ₂ O ₃ ).

The resulting slurry was coated on a copper foil (17 μm) using a 125 μm wet thickness, and then dried at 70 ° C. for 2 hours to prepare an electrode. The round electrode is drilled and dried in a small vacuum oven at 150 ° C. for 3 hours. The electrode is electrochemically tested against metallic lithium using a coin cell prepared in a glove box (under anhydrous argon atmosphere). The electrolyte used was LiPF ₆ (1 M) (Semichem) in a mixture of EC / DEC (50/50 wt%) + 10% FEC + 2% VC. Coin cells are tested in CC mode at 10 mV to 1.5 V at a C-speed of C / 5 (meaning full charge or discharge of 3570 mAh / g of active material within 5 hours). The results are presented in FIG. 7.

The inventors clearly recognize that the behavior of the electrode is improved with a coating of alumina (line 1): after 100 cycles, the delivered capacity is maintained at about 2400 mAh / g compared to 1000 mAh / g for intact silicon (Line 2). It has also been found that coatings thinner than 1 nm do not have the desired effect.

Control Example 1: Alumina coated silicon with high thickness alumina

Alumina coated silicon was prepared by the ALD process as in Example 1. For the preparation of this powder 25 cycles (compared to 6 cycles in Example 1) (TMA followed by water) are used. The alumina layer has a thickness of 12 nm. The BET of the surface is reduced to 16 m 2 / g, and the amount of alumina is measured at 8% by weight of powder. The slurry and battery were prepared as in Example 1, and the results are presented in FIG. 8. The capacity is less than 500 mAh / g from the first cycle, and this capacity drops in the next cycle. These results clearly show that it is important to have a thin layer on the surface of the silicon to enable the electrochemical reaction.

Example 2: Alumina coated silicon particles and nanowires

In this example, an alumina coating is applied by atomic layer deposition (ALD) on Si particles and nanowires prepared according to International Patent Application Publication No. WO2012-000854 and having an oxygen content of less than 4% by weight. The synthetic procedure is described in Example 1.

Microscopic observation photos (see FIG. 9) show a homogeneous and thin conformal alumina coating on the surface of the silicon particles. The coated powder is dispersed in ethanol and then placed on a carbon grid mounted on a Cu support. The grinding step was omitted in the sample preparation to avoid damage to the powder. EFTEM maps showing silicon, alumina and oxygen contrast are obtained at 300 kV using a Philips CM30-FEG microscope (see FIG. 9). The amount of aluminum is measured by ICP and a value of 2% by weight is calculated. As in Example 1, it can be demonstrated that the silicon is completely covered with another material (Al ₂ 0 ₃ ) by measuring the viscosity increase of the CMC powder solution over time.

The zeta potential is measured according to the following procedure: Both a 2% by weight reference powder in 150 ml demineralized water and an alumina coated silicon nanowire suspension are prepared by sonication (120 seconds at 225 W). The zeta potential of this suspension in an aqueous medium is measured with the Zeta Probe Analyzer ™ of Colloidal Dynamics. The sample is automatically titrated from neutral pH to acidic pH with 0.5 M HCl and automatically titrated to a higher basic pH with 0.5 M NaOH.

It is possible to clearly measure the high negative surface charge on the nanowire (see line 2 in Fig. 10). Zeta potential is negative from pH 8 to 2. In the case of alumina coated silicon nanowires, the powder has a large amount of zeta potential from pH 8 to at least pH 2 (line 1 in FIG. 10).

Example 3: Acid-base treatment of silicon surface

A 2 wt% nano-silicon suspension in 150 ml demineralized water is prepared by sonication (120 sec at 225 W). The nano-silicon is prepared according to International Patent Application Publication No. WO2012-000858 and has a BET of 25 m 2 / g, an oxygen content of less than 4% by weight, particle size defined as 80 nm <D80 <200 nm, (by plasma The silicon powder generated typically has an aluminum contamination of at least 0.1% by weight (this contamination is concentrated on the surface of the particles) and an initial negative zeta potential (defined at pH in water). A known amount of 0.5 M HCl is added to the suspension to lower the pH to 2. Thereafter, 0.5 M NaOH is added to increase the pH of the suspension back to pH 4. The zeta potential of this suspension in an aqueous medium is measured with the Zeta Probe Analyzer ™ of Colloidal Dynamics. Since the zeta potential of +12 mV is measured, the measured charge for these particles is a positive charge.

Figure 11 shows the charge change of the suspension during acid-base treatment. Measurements are performed using the Colloidal Dynamics ZetaProbe Analyzer ™ and a solution of 0.5 M HCl and 0.5 M NaOH. During acid treatment, a steep decrease in surface charge is observed below pH 5 (interpreted by a decrease in the absolute value of the zeta potential), which decreases probably protonation of silanol groups on the oxidized Si surface and freeing aluminum ions. This may be due to the dissolution of aluminum compound contaminants. During reverse titration (= base treatment), the zeta potential becomes positive at pH 3.4 to pH 4.9. During the addition of the base, precipitation of alumina occurs at the surface of the electrode, thus creating a positive charge. Because the amount of alumina is small, the coverage is not complete, which explains the behavior of the surface, where the dislocation is negative at a pH above 5.

To prepare the electrode, the first step is to prepare a 2.4% Na-CMC solution by dissolving 2.4% Na-CMC overnight and then adjusting its pH to the pH of a pre-made silicon suspension. Conductive carbon is added and the mixture is stirred for 20 minutes using a high-shear mixer. Once a good dispersion of conductive carbon is obtained, an active material suspension (treated with silicon) is added and the resulting slurry is stirred again for 30 minutes using a high-shear mixer. The slurry was prepared with a final composition of 50% by weight of this powder, 25% by weight of a Na-CMC binder (molecular weight <200000) and 25% by weight of a conductive additive (Super C65, Timcal).

The resulting slurry was coated on a copper foil (17 μm) using a 125 μm wet thickness, and then dried at 70 ° C. for 2 hours to prepare an electrode. The round electrode is drilled and dried in a small vacuum oven at 150 ° C. for 3 hours. The electrode is electrochemically tested against metallic lithium using a coin cell prepared in a glove box (under anhydrous argon atmosphere). The electrolyte used is LiPF ₆ (1 M) (Semichem) in a mixture of EC / DEC (50/50 wt%) + 10% FEC + 2% VC. Coin cells are tested in CC mode at 10 mV to 1.5 V at a C-speed of C / 5 (meaning full charge or discharge of 3570 mAh / g of active material within 5 hours). The results are shown in FIG. 12, comparing the increase in capacity during cycling of the intact nano-silicon powder 2 with the increase in the case of alumina coated silicon 1.

The inventors clearly recognize that the electrode's behavior is improved by acid / base treatment in the presence of aluminum ions: after 100 cycles, the delivered capacity is about 3000 mAh / g compared to 1000 mAh / g for intact silicon Is maintained as.

Example 4: Silane coated silicon

12 g of nano-silicon particles (prepared according to International Patent Application Publication No. WO2012-000858), NH ₄ OH, H ₂ 0 and C ₂ H ₅ OH (pure ethanol) in a ratio of 1:10:14, respectively. Disperse in the containing 1000 cm ³ solution. Ammonium hydroxide (NH ₄ OH, 30%) was supplied by JT Baker. The suspension is sonicated for 20 minutes and stirred further overnight. Then, 6 g of APTS (silicon alkoxide: 3-aminopropyltriethoxysilane) is added to the suspension, sonicated for 10 minutes and stirred further overnight. APTS was purchased from Sigma Aldrich. The particles settle and the mother liquor is removed. Then, the amine-modified Si particles are washed three times with ethanol, and then dried in a vacuum oven at 60 ° C overnight.

The effect of surface modification is evaluated by the zeta potential (ZP) found from electrophoretic mobility measurements over a wide range of pH values. The surface zeta potential of this powder is investigated using Zeta PALS from Brookhaven Instruments. A dispersion containing 0.25 mg / cm ³ of modified silicon is prepared by dissolving the powder in 0.001 mol / L of KCl. To keep the ionic strength constant, the pH is adjusted using 0.1 mol / L KOH and 0.1 mol / L HCl solution. By testing different weight ratios of APTS: Si, it was concluded that a ratio of 1: 2 or higher is recommended to obtain positive charges on the particle surface.

FIG. 13 shows the zeta potential of amine modified silicon (where weight ratio of APTS: Si = 5: 4) (line 1) and intact silicon (line 2) as a function of pH at constant ionic strength. At pH values below 7 (amine treated particles have an isoelectric point at neutral pH), the success of the surface modification is demonstrated by changing the surface charge of the particles from negative to positive. On the other hand, intact Si particles are negatively charged over a pH range of 3 to 11. All silicon particles treated with APTS have a similar zeta potential profile when the weight ratio of APTS: Si is higher than 1: 2.

APTS is one of the examples of cationic silanes that can be used to generate positive charges. Derivatives of APTS (eg, aminomethyltriethoxysilane, 2-aminoethyltriethoxysilane, aminotriethoxysilane, 3-aminopropyltrimethoxysilane), triethoxy (3-isocyanatopropyl) The same effect can be obtained by using a derivative of silane or a derivative of N- [3- (trimethoxysilyl) propyl] aniline.

Example 5: Adsorption of nano-alumina particles onto silicon particles

A suspension of 1% by weight nano-silicon (prepared according to International Patent Application Publication No. WO2012-000858) in 100 ml of demineralized water is prepared by sonication (120 seconds at 225 W). To obtain an Al ₂ O ₃ / Si ratio of 2 or more, a known amount of 2 wt% Al ₂ O ₃ nanoparticles dispersed in water (commercially available: DISPARAL P2, Sasol; particle size <30 nm ) Is added to this suspension. In this example, 5% by weight of Al ₂ O ₃ nanoparticles are added. The combined dispersion is placed on a rollerbank for 30 minutes. Below the alumina / silicon weight ratio of 2/1, the agglomeration (silicon particles together with the alumina adsorbed particles) charge remains negative, the minimum amount of alumina particles being recommended to actually cover sufficient silicon surfaces and have an average charge of the amount of aggregation. . Analysis of porosity shows that some microporosity (<0.01 cc / g) appears after treatment. It is probably formed between nanoparticles of alumina.

After this mixing, the pH of the solution is 6 and the zeta potential of this suspension in an aqueous medium is measured with the Zeta Probe Analyzer ™ of Colloidal Dynamics. Since the zeta potential of +45 mV is measured, the measured charge on these particles is a positive charge. This value shows that the alumina colloid was adsorbed on the surface of the silicon particles. The combined dispersion is then dried under vacuum through a rotary evaporator heated to 80 ° C. for 10 hours.

The zeta potential is measured according to the following procedure: Both 1% by weight of the nano-silicon powder and the treated silicon powder suspension in 100 ml of demineralized water are prepared by sonication (120 seconds at 225 W). The zeta potential of these suspensions in an aqueous medium is measured with a Colloidal Dynamics Zeta Probe Analyzer ™. The sample is automatically titrated from neutral pH to acidic pH with 0.5 M HCl and automatically titrated to a higher basic pH with 0.5 M NaOH. Since the zeta potential is measured at 53 mV, the initial charge of the treated silicon is a positive charge. Thus, this value shows that the adsorption of nanoparticles of alumina is maintained during the drying process. The high negative surface charge on the nano-silicon powder can be clearly measured (see line 2 in Figure 14). The zeta potential is negative at pH 2 to at least pH 5 for intact silicon, but the treated silicon powder has a positive zeta potential at pH 9.5 to at least pH 2.5 (line 1 in FIG. 14).

The slurry and battery were prepared as in Example 1, and the results of the coin cell test are shown in FIG. 15. The inventors clearly recognize that the behavior of the electrode is improved by adsorption of nano-alumina particles (line 1): the initial delivered capacity is similar to the theoretical capacity of the material, and the delivered capacity after 100 cycles remains intact It remains at about 2200 mAh / g compared to 1000 mAh / g for silicon (see line 2 in Figure 7).

Example 6: Adsorption of cationic polymers

For adsorption of cationic polymers, known dispersants are used: (C ₂ H ₄ NH) _n or polyethylene-imine (PEI) of the formula:

This polymer is a branched polymer containing primary, secondary and tertiary functional groups. Nitrogen can be protonated to produce highly positively charged polymers. This also offers the advantage of being soluble in water.

A suspension of 1% by weight nano-silicon (prepared according to International Patent Application Publication No. WO2012-000858) in 100 ml of demineralized water is prepared by sonication (120 seconds at 225 W). A predetermined amount of 1% by weight PEI dispersed in water (PEI 10 kmol / g, pH adjusted to 6) is added to this suspension. The combined dispersion is placed on a roller bank for 30 minutes. After this mixing, the zeta potential of the suspension in an aqueous medium is measured with the Zeta Probe Analyzer ™ of Colloidal Dynamics. Since the zeta potential of +30 mV is measured, the measured charge on the particle is a positive charge. This value shows that the polymer chain is adsorbed on the surface of the silicon particles. To obtain a positive effect, a PEI / Si weight ratio of 0.35 / 1 or higher or a PEI mass of 14 mg or more per m 2 of silicon surface is recommended. This value shows that in Example 5 a significantly lower mass of PEI than in the case of nano-alumina is needed to obtain positive charges. The combined dispersion is then dried under vacuum through a rotary evaporator heated to 80 ° C. for 10 hours.

The zeta potential is measured according to the following procedure: Both 1% by weight of the nano-silicon powder and the treated silicon powder suspension in 100 ml of demineralized water are prepared by sonication (120 seconds at 225 W). The zeta potential of these suspensions in an aqueous medium is measured with a Colloidal Dynamics Zeta Probe Analyzer ™. The sample is automatically titrated from neutral pH to acidic pH with 0.5 M HCl and automatically titrated to a higher basic pH with 0.5 M NaOH. Since the zeta potential is measured at +35 mV, the initial charge of the treated silicon is a positive charge. Thus, this value shows that adsorption of PEI is maintained during the drying process.

The high negative surface charge on the nano-silicon powder can be clearly measured (see line 2 in Figure 16). The zeta potential is negative at pH 12 to pH 2 for intact silicon, but the treated silicon powder has a positive zeta potential at pH 6 to at least pH 2.5 (line 1 in FIG. 16).

These effects are pH dependent primary, secondary or tertiary amines such as octenidine dihydrochloride, poly (4-vinylpyridine), poly (2-vinylpyridine N-oxide), poly (N-vinylpyrrolidone) ) And other cationic surfactants and polymers.

The slurry and battery were prepared as in Example 1. Adsorption of the cationic polymer improves the capacity retention of the electrode: after 100 cycles, the delivered capacity is maintained at a level above 1500 mAh / g compared to 1000 mAh / g for intact silicon (line 2 in FIG. 7). .

Example 7: Adsorption of cations on silicon particles

A suspension of 1% by weight nano-silicon (prepared according to International Patent Application Publication No. WO2012-000858) in 100 ml of demineralized water is prepared by sonication (120 seconds at 225 W). At least 26 mg of Al ³⁺ (in the form of AlCl ₃ salt) is added to this suspension. This leads to an Al / Si ratio of 0.026 or more or 1 mg or more of Al per m2 of silicon. The combined dispersion is placed on a roller bank for 30 minutes. The combined dispersion is then dried under vacuum through a rotary evaporator heated to 80 ° C. for 10 hours.

The zeta potential is measured according to the following procedure: Both 1% by weight of the nano-silicon powder and the treated silicon powder suspension in 100 ml of demineralized water are prepared by sonication (120 seconds at 225 W). The zeta potential of these suspensions in an aqueous medium is measured with the Zeta Probe Analyzer ™ of Colloidal Dynamics. The initial pH of this solution is 5.3 and the zeta potential is +40 mV. Then, the sample is automatically titrated from neutral pH to acidic pH using 0.5 M HCl and automatically titrated to a higher basic pH using 0.5 M NaOH. The redispersed and treated powder has a positive value of 2 to 7 with a zeta potential of 2 to 5 while having a stable value of +65 mV (line 1 in FIG. 17). The zeta potential is negative at least pH 5 to 2 for natural silicon (line 2 in FIG. 17).

The slurry and battery were prepared as in Example 1, and the results are presented in FIG. 18 (capacity in mAh / g vs. number of cycles). The inventors clearly recognize that the electrode behavior is improved by adsorption of cations (line 1): after 100 cycles, the delivered capacity is maintained at about 1950 mAh / g compared to 1000 mAh / g for intact silicon It becomes (line 2 of FIG. 7).

Similar results can be obtained with water-soluble aluminum salts other than AlCl ₃ or Sb, Ti and Zn (all cationic polyvalent metals).

Example 8a: Alumina coated silicon: Change of specific surface area

In this example, 77K after being prepared according to International Patent Application Publication No. WO2012-000858 and preheated for 1 hour under a flow of argon at 150 ° C. with a BET of 40 m 2 / g with an open pore volume of less than 0.001 cc / g. 5 g of nano-silicon powder having an initial negative zeta potential (defined at pH 7 in water) and an oxygen content of less than 4% by weight), as measured by an ASAP device via isothermal adsorption-desorption of N ₂ at Was used and treated as in Example 1.

Microscopic observation pictures show a homogeneous and thin (3 nm) conformal alumina coating on the silicon particle surface. The BET surface area of this powder was preheated at 150 ° C. under a flow of argon for 1 hour and then 40 m 2 / g (BET after ALD treatment) with a void volume of less than 0.001 cc / g from the result of isothermal adsorption-desorption of N ₂ at 77K. (No change). The amount of aluminum is measured by ICP and a value of 3.4% by weight is calculated. The zeta potential of the generated material is measured according to the following procedure: Both a reference 2% by weight nano-silicon powder and alumina coated silicon suspension in 150 ml of demineralized water are prepared by sonication (120 seconds at 225 W). The zeta potential of this suspension in an aqueous medium is measured with the Zeta Probe Analyzer ™ of Colloidal Dynamics. The sample is automatically titrated from neutral pH to acidic pH with 0.5 M HCl and automatically titrated to a higher basic pH with 0.5 M NaOH. The high negative surface charge on the nano-silicon powder can be clearly measured (see line 2 in Figure 19). Zeta potential is negative at pH 6 to pH 2. For alumina coated silicon, the powder has a positive zeta potential at least between pH 9 and at least pH 2.5 (line 1 in FIG. 19).

Electrodes were prepared and tested as in Example 1. The results show that the electrode behavior is improved by coating of alumina: after 100 cycles, the delivered capacity is maintained at about 2500 mAh / g compared to 1000 mAh / g for intact silicon (line 2 in FIG. 7). Reference). It has also been found that coatings thinner than 1 nm do not exhibit the desired effect.

Example 8b: Alumina coated silicon: Change of specific surface area

In this example, 1 m 2 / g of BET (preheated for 1 hour under a flow of argon at 150 ° C.) with an open pore volume of less than 0.001 cc / g, followed by isothermal adsorption-desorption of N ₂ at 77K to the ASAP device. Measurement performed by), 1.5 g of commercial micrometer sized powder (Aldrich) with an oxygen content of less than 4% by weight and an initial negative zeta potential (defined at pH 7 in water) was used as in Example 1. And process it.

Microscopic observation pictures show a homogeneous and thin (3 nm) conformal alumina coating on the silicon particle surface. The zeta potential of the generated material is measured as in Example 8a. The negative surface charge on the silicon powder can be clearly measured. Zeta potential is negative at pH 6 to pH 2. For alumina coated silicon, the powder has a positive zeta potential at least between pH 7 and at least pH 2.5.

Example 9: Alumina coated silicon monoxide

In this example, 5 consisting of a mixture of nanometer-sized Si and SiO ₂ and having a BET of 2 m 2 / g, an oxygen content of about 32% by weight, and an initial negative zeta potential (defined at pH 7 in water). g of micrometer silicon monoxide powder is used and treated as in Example 1.

Microscopic observation pictures show a homogeneous and thin (3 nm) conformal alumina coating on the silicon particle surface. The BET surface area and oxygen content of this powder did not change during ALD treatment. The zeta potential of the generated material is measured according to the following procedure: Both a reference 2% by weight nano-silicon powder and alumina coated silicon suspension in 150 ml of demineralized water are prepared by sonication (120 seconds at 225 W). The zeta potential of this suspension in an aqueous medium is measured with the Zeta Probe Analyzer ™ of Colloidal Dynamics. The sample is automatically titrated from neutral pH to acidic pH with 0.5 M HCl and automatically titrated to a higher basic pH with 0.5 M NaOH. A high negative surface charge on a micrometer-sized silicon monoxide powder can be clearly measured (see line 2 in Figure 20). Zeta potential is negative at pH 7 to at least pH 4. In the case of alumina coated silicon monoxide, the powder has a positive zeta potential at least between pH 3 and at least pH 6.8 (line 1 in FIG. 20).

Example 10: Alumina and carbon coated silicon

In this embodiment, a carbon core made according to International Patent Application Publication No. WO2012-000858 with a carbon coating prepared by CVD (chemical vapor deposition of toluene) technique and a BET of 20 m 2 / g, about 4% by weight A 5 g carbon coated nanometer sized silicon powder having an oxygen content of and an initial zeta potential close to zero (defined at pH 7 in water) is used and treated as in Example 1. After ALD treatment, particle characteristics (alumina layer thickness, BET and oxygen content) are similar to the previous examples. The increase in positive charge can be measured by zeta potential measurement (performed as in the previous example).

Example 11: Adsorption of nanoparticles on silicon surface: In (OH) ₃ Nanoparticles

A suspension of 1% by weight nano-silicon (prepared according to International Patent Application Publication No. WO2012-000858) in 100 ml of demineralized water is prepared by sonication (120 seconds at 225 W). A known amount of 1% by weight In (OH) ₃ nanoparticles (commercially available: particle size <30 nm) dispersed in water is added to this suspension to obtain an In (OH) ₃ / Si ratio of 0.02 or more. . The combined dispersion is placed on a roller bank for 30 minutes. Under this indium hydroxide / silicon weight ratio of 0.02, the aggregation (silicon particles together with the adsorbed particles) charge remains negative, the minimum amount of particles being recommended to actually cover sufficient silicon surfaces and have an average charge of the amount of aggregation.

Example 12: Adsorption of nanoparticles on silicon surface: Nanoparticles of alumina treated silica

A suspension of 1% by weight nano-silicon (prepared according to International Patent Application Publication No. WO2012-000858) in 100 ml of demineralized water is prepared by sonication (120 seconds at 225 W). A known amount of 2 wt% alumina treated silica (Levasil 200s) nanoparticles dispersed in water is added to this suspension to obtain a treated Si0 ₂ / Si ratio of 1.5 or higher. The combined dispersion is placed on a roller bank for 30 minutes. Above this treated Si0 ₂ / silicon weight ratio of 1.5, the agglomeration (silicon particles together with the adsorbed particles) charge remains negative, a minimum amount of particles is recommended to actually cover sufficient silicon surfaces and have an average charge of the amount of aggregation. .

The slurry and battery were prepared as in Example 1, and the results are presented in FIG. 15 (line 2). The inventors clearly recognize that the behavior of the electrode is improved by adsorption of this type of nanoparticles: after 100 cycles, the delivered capacity is maintained at about 1600 mAh / g compared to 1000 mAh / g for intact silicon It becomes (line 2 of FIG. 7).

Example 13: Adsorption of nanoparticles on silicon surface: Nanoparticles of iron oxide

A suspension of 1% by weight nano-silicon (prepared according to International Patent Application Publication No. WO2012-000858) in 100 ml of demineralized water is prepared by sonication (120 seconds at 225 W). At least ₂ % by weight of a known amount of iron oxide (commercially available, particle size 20.25 nm) nanoparticles dispersed in water is added to this suspension to obtain a Fe ₂ 0 ₃ / Si ratio of 2 or more. The combined dispersion is placed on a roller bank for 30 minutes. Below this iron oxide / silicon weight ratio of 2, the agglomeration (silicon particles together with the adsorbed particles) charge remains negative, with a minimum amount of particles recommended to actually cover sufficient silicon surfaces and have an average charge of the amount of aggregation. Negative surface charges on nanometer-sized silicon powders can be clearly measured. Zeta potential is negative at pH 4.5 to at least 9. For iron oxide coated silicon, the powder has a positive zeta potential at least between pH 2 and pH 8.

The slurry and battery were prepared as in Example 1. The inventors clearly recognize that the electrode behavior is improved by adsorption of nanoparticles of iron oxide: after 100 cycles, the delivered capacity is maintained at about 2000 mAh / g compared to 1000 mAh / g for intact silicon. (Line 2 in FIG. 7). At the same time, we can also observe that the adsorbed particles participate in energy storage. Indeed, the inventors know that iron oxide nanoparticles can be reversibly reduced depending on the conversion process.

Example 14: Adsorption of nanoparticles on silicon surface: nanoparticles of magnesium oxide

A suspension of 1% by weight nano-silicon (prepared according to International Patent Application Publication No. WO2012-000858) in 100 ml of demineralized water is prepared by sonication (120 seconds at 225 W). At least 2% by weight of magnesium oxide (commercially available) nanoparticles in a known amount dispersed in water are added to this suspension to obtain a MgO / Si ratio of 1 or more. The combined dispersion is placed on a roller bank for 30 minutes. Below this MgO / silicon weight ratio, the agglomeration (silicon particles together with the adsorbed particles) charge remains negative, and a minimum amount of particles is recommended to actually cover enough silicon surfaces and have an average charge of the amount of aggregation. Negative surface charges on nanometer-sized silicon powders can be clearly measured. Zeta potential is negative at least at pH 3.5 to at least 9. For iron oxide coated silicon, the powder has a positive zeta potential at least between pH 2 and at least pH 9.

Claims (38)

A negative electrode material for a lithium rechargeable battery, comprising a core comprising silicon, wherein the surface of the core is at least partially covered with a coating composed of inorganic nanoparticles, the nanoparticles forming a first coating layer on the core, and The first coating layer has a thickness of less than 10 nm, the material has a positive zeta potential in at least a portion of the pH range consisting of pH 3.5 to pH 9.5, and the core has a cathode having an average particle size of 20 nm to 200 nm material. The negative electrode material according to claim 1, wherein the inorganic nanoparticle is one of aluminum, aluminum compounds, zinc, zinc compounds, antimony and antimony compounds. The negative electrode material according to claim 2, wherein the aluminum compound is Al ₂ 0 ₃ , the zinc compound is zinc oxide, and the antimony compound is antimony oxide. According to any one of claims 1 to 3, The negative electrode material further comprises a second coating layer comprising carbon or aluminum, the second coating layer between the core and the inorganic nanoparticles forming the first coating layer Located cathode material. The negative electrode material according to claim 1, wherein the first coating layer has a thickness between 1 nm and 5 nm. The negative electrode material according to claim 1, wherein the first coating layer is conformal or porous. The negative electrode material according to claim 4, wherein one or both of the first coating layer and the second coating layer are electrochemically active. The negative electrode material according to claim 1, wherein the nanoparticles include a precursor material that is easily converted to one of aluminum, zinc, and antimony by reduction. A negative electrode material for a lithium rechargeable battery, comprising a core comprising silicon, wherein the surface of the core is at least partially covered with adsorbed cationic polyvalent metal ions, and the material has a pH ranging from pH 3.5 to pH 9.5. A cathode material having a positive zeta potential in at least a portion, the core having an average particle size of 20 nm to 200 nm. 10. The anode material of claim 9, wherein the metal ion is at least one of the group consisting of Al-ion, Sb-ion, Fe-ion, Ti-ion and Zn-ion. A negative electrode material for a lithium rechargeable battery, comprising a core comprising silicon, wherein the surface of the core is at least partially covered with adsorbed organic molecules, and the material is in at least a portion of a pH range consisting of pH 3.5 to pH 9.5. Cathode material having a positive zeta potential and the core having an average particle size of 20 nm to 200 nm. A negative electrode material for a lithium rechargeable battery comprising a core comprising silicon, wherein the surface of the core is at least partially covered with silanol groups covalently bonded to an amino functional metal compound, the metal compound being Si, Al and Ti. One or more of the group consisting of, the material has a positive zeta potential in at least a portion of the pH range consisting of pH 3.5 to pH 9.5, the core is a negative electrode material having an average particle size of 20 nm to 200 nm. A negative electrode material for a lithium rechargeable battery, comprising a core comprising silicon, wherein the surface of the core is at least partially covered with adsorbed nanoparticles of cationic polyvalent metal oxide, the material consisting of pH 3.5 to pH 9.5 Cathode material having a positive zeta potential in at least a portion of the pH range, the core having an average particle size of 20 nm to 200 nm. The method of claim 13, wherein the metal oxide is at least one of the group consisting of Al-oxide, Ca-oxide, Mg-oxide, Pb-oxide, Sb-oxide, Fe-oxide, Ti-oxide, Zn-oxide and In-hydroxide. Cathode material. The negative electrode material according to claim 1, comprising a particle or a mixture of particles and wires, both particles and wires are nano-sized, wherein the average particle size of the particles is at least 5 times the average width of the wires. The method of claim 1, wherein the core,
-Pure silicon; or
-Silicon monoxide powder comprising a mixture of nanometer-sized Si and SiO ₂ ; or
Silicon having a SiO _x surface layer (0 <x <2) having an average thickness of 0.5 nm to 10 nm; or
-The formula SiO _x . (M _a O _b ) _y (where 0 <x <1, 0 ≤ y <1, a and b are selected to provide electrical neutrality, M is Ca, Mg, Li, Al and A uniform mixture of silicon oxide and metal oxide), which is selected from the group consisting of Zr); or
-Alloy Si-X (where X is one or more metals selected from the group consisting of Sn, Ti, Fe, Ni, Cu, Co and Al)
Cathode material consisting of. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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