Composite powder for use in battery negative electrodes and batteries containing such composite powders

Abstract

1. A composite powder for use in a battery anode comprising composite particles, the composite particles comprising a carbon matrix material and silicon-based particles embedded in the carbon matrix material, the composite powder having a Raman spectrum with a D band and a D′ band both corresponding to contributions from the carbon matrix material and a Raman spectrum at 1330 cm -1 ~1360cm -1 I D and 1600 cm -1 ~1620cm -1 I D’ and the ratio I D / I D’ is at least 0.9 and at most 4.0.

Description

[Technical Field]

[0001] The present invention relates to composite powders suitable for use in battery negative electrodes, and to batteries containing such composite powders. [Background technology]

[0002] Lithium-ion (Li-ion) batteries are currently the most powerful batteries and have already become the standard for portable electronic devices. In addition, these batteries are now rapidly expanding into other industries, such as automotive and energy storage. The enabling advantage of such batteries is their high energy density combined with good power performance.

[0003] A Li-ion battery typically comprises several so-called Li-ion cells, which in turn comprise a positive electrode, also called a cathode, which is immersed in an electrolyte, a negative electrode, also called an anode, and a separator. The Li-ion cells most frequently used in portable applications are developed using electrochemically active materials such as lithium cobalt oxide or lithium nickel manganese cobalt oxide in the cathode and natural or synthetic graphite in the anode.

[0004] It is known that the active material in the anode is one of the key limiting factors affecting battery performance, especially the energy density of the battery. Therefore, the use of silicon-containing electrochemically active materials in the negative electrode has been investigated for many years to improve energy density.

[0005] In the art, the performance of batteries containing Si-based electrochemically active powders is generally quantified by the so-called full cell cycle life, which is defined as the number of times or cycles that a cell containing such material can be charged and discharged until it reaches 70% of its initial discharge capacity. Therefore, most research on silicon-based electrochemically active powders focuses on improving this cycle life.

[0006] A drawback of using silicon-based electrochemically active materials in anodes is their large volume expansion during charging, for example, as much as 300% when lithium ions are fully incorporated into the anode's active material by alloying or intercalation (a process often referred to as lithiation). The large volume expansion of silicon-based materials during lithium incorporation can induce stresses in the silicon-based particles, which can eventually lead to mechanical degradation of the silicon material. The repeated mechanical degradation of silicon-based electrochemically active materials, as cyclically cycled during charging and discharging of Li-ion batteries, can reduce the battery's life to unacceptable levels.

[0007] Another adverse effect associated with silicon is that a thick SEI, or solid electrolyte interface, can form on the anode. The SEI is a complex reaction product between the electrolyte and lithium, which results in a loss of lithium availability for electrochemical reactions, leading to poor cycling performance, which is capacity loss with each charge-discharge cycle. A thick SEI can also increase the battery's electrical resistance, thereby limiting its ability to discharge and charge at high currents.

[0008] In principle, SEI formation is a self-terminating process that stops as soon as a "passivation layer" forms on the surface of the silicon-based material. However, due to the volume expansion of the silicon-based particles, both the silicon-based particles and the SEI can be damaged during discharge (lithiation) and recharge (delithiation), thereby freeing new silicon surfaces and leading to the initiation of new SEI formation.

[0009] To overcome the above drawbacks, composite powders are typically used. In these composite powders, nano-sized silicon-based particles are mixed with at least one component suitable for protecting the silicon-based particles from electrolyte decomposition and for accommodating volume changes. Such a component may be a carbon-based material, preferably forming a matrix.

[0010] The composite powder usually further contains graphite particles in order to adjust the specific capacity to a practical level of 500 mAh / g to 1500 mAh / g.

[0011] Such composite powders are described, for example, in U.S. Patent Application Publication No. 2019 / 0198863, which discloses an anode active material comprising a composite of a Si-based or Sn-based material and a carbon-based material, and which has a D peak (1360 cm -1 ~1370cm -1 ) peak intensity (I D ) of the D' peak of carbon-based materials (1620 cm -1 ~1625cm -1 ) peak intensity (I D’ ) to the Raman spectrum peak intensity ratio (I D / I D’ ) is 4.5 to 10.

[0012] British Patent No. 2563455 discloses a granular material consisting of a plurality of composite particles, the composite particles comprising a plurality of silicon nanoparticles dispersed within a conductive carbon matrix, and the contribution of the conductive carbon matrix in the Raman spectrum of the granular material is identified by a large G band and a prominent D band. British Patent No. 2563455 also identifies the presence of a D' band as the ratio of the intensities of the D band and the D' band, I D / I D’ There is no mention of any technical effect related to either of these.

[0013] WO2022074031 discloses a powder of carbonaceous matrix material particles with silicon-based subparticles dispersed therein. WO2022074031 does not disclose Raman data.

[0014] European Patent No. 3113261 discloses a negative electrode material for a non-aqueous electrolyte secondary battery, the negative electrode material comprising a conductive powder composed of silicon-based active material particles coated with a conductive carbon film, the conductive carbon film having a peak intensity ratio l of 1.1 or less. D / l G [l Dis the peak intensity of the D band, and l G is the peak intensity of the G band, and the D band and the G band are obtained from the Raman spectrum of the conductive carbon film. In European Patent No. 3113261, the existence of the D' band is also confirmed by the ratio of the intensities of the D band and the D' band, I D / I D’ There is no mention of any technical effect related to either of these.

[0015] In WO 2010 / 065739, up to four bands, i.e., at about 1360 cm -1 (D band), approximately 1580cm -1 (G band), approx. 1620cm -1 (D' band), and approximately 2660 cm -1 WO 2010 / 065739 discloses an article of manufacture comprising a carbon-containing matrix having a Raman spectrum with a band at the D band and the D′ band (DP band). D / I D’ Neither the technical effects associated with silicon-based particles embedded in a carbon-containing matrix are mentioned.

[0016] Despite the use of such composite powders, there is still room for improvement in the performance of batteries containing Si-based electrochemically active powders. In particular, existing composite powders cannot achieve both high capacity and long cycle life, which are essential for batteries, especially for electric vehicles. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] US Patent Application Publication No. 2019 / 0198863 [Patent Document 2] British Patent No. 2563455 [Patent Document 3] International Publication No. 2022 / 074031 [Patent Document 4] European Patent No. 3113261 [Patent Document 5] International Publication No. 2010 / 065739 Summary of the Invention [Problem to be solved by the invention]

[0018] It is an object of the present invention to provide a composite powder comprising composite particles, the composite particles comprising a carbon matrix material having silicon-based particles embedded therein, which, once used in a battery anode, is advantageous in that it can achieve high capacity combined with long cycle life. [Means for solving the problem]

[0019] This object is achieved by providing a composite powder according to the present invention, which, when used in the negative electrode of a battery, makes it possible to achieve a high capacity combined with a long cycle life, as demonstrated in Examples 1 to 3 in comparison with Comparative Examples 1 to 3. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a Raman spectrum of a graphite material. [Figure 2] 1 is a Raman spectrum of composite powder E1 with peak fitting. DETAILED DESCRIPTION OF THE INVENTION

[0021] In the following detailed description, preferred embodiments are described in detail to facilitate the practice of the present invention. While the present invention is described with reference to these specific preferred embodiments, it will be understood that the present invention is not limited to these preferred embodiments. On the contrary, the present invention encompasses numerous alternatives, modifications, and equivalents, as will become apparent from a consideration of the following detailed description and the accompanying drawings.

[0022] In a first aspect, the present invention provides a composite powder for use in a battery anode comprising composite particles, the composite particles comprising a carbon matrix material and silicon-based particles embedded in the carbon matrix material, the composite powder having a Raman spectrum obtained by Raman scattering, the Raman spectrum including a D band and a D′ band both corresponding to contributions from the carbon matrix material and having a Raman spectrum at 1330 cm -1 ~1360cm -1 I D and 1600 cm -1 ~1620cm -1 I D’ and the ratio I D / I D’ is at least 0.9 and at most 4.0.

[0023] maximum strength I D is preferably 1330 cm -1 ~1359cm -1 , more preferably 1330 cm -1 ~1357cm -1 , and even more preferably 1330 cm -1 ~1355cm -1 and the maximum intensity I D’ is preferably 1600 cm -1 ~1619cm -1 , more preferably 1600 cm -1 ~1617cm -1 , and even more preferably 1600 cm -1 ~1615cm -1 is.

[0024] Preferably, the composite particles consist of a carbon matrix material in which silicon-based particles are embedded.

[0025] "Composite particles comprising a carbon matrix material and silicon-based particles embedded in the carbon matrix material" means that the composite particles are larger in size, on average, than the silicon-based particles because the composite particles comprise silicon-based particles. The composite particles are typically micrometer-sized, while the silicon-based particles are typically nanometer-sized.

[0026] "Silicon-based particles embedded in said carbon matrix material" means that at least 50% of the surface of the silicon-based particles is coated with the carbon matrix material, preferably at least 75% of the surface of the silicon-based particles is coated with the carbon matrix material, and preferably the silicon-based particles are completely coated with the carbon matrix material to ensure adequate protection against reaction with the electrolyte during cycling. In other words, the silicon-based particles and the carbon matrix material are not mixed together, since adequate coverage of the surface of the silicon-based particles cannot be obtained in that way.

[0027] The silicon-based particles embedded in the carbon matrix material form agglomerates with a size of less than 1 μm or do not form agglomerates at all, and therefore in the composite powder according to the invention, the silicon-based particles are preferably in contact only with each other and / or with the carbon matrix material.

[0028] The silicon-based particles may have any shape, for example, substantially spherical, but may also have irregular shapes, rods, plates, etc. In the silicon-based particles, the silicon is present mostly as silicon metal, to which small amounts of other elements may be added to improve properties, or the silicon may contain some impurities such as oxygen or trace metals. Considering all elements other than oxygen, the average silicon content in such silicon-based particles is preferably 80 wt% or more, more preferably 90 wt% or more, based on the total weight of the silicon-based particles.

[0029] In the Raman spectrum of graphite materials, such as the carbon matrix material of the composite powders of the present invention, the most prominent feature is typically at about 1580 cm -1 The so-called G band, which appears at approximately 1350 cm -1 The D band appears at approximately 1610 cm -1 The D' band appears at approximately 2700 cm -1The G' band (also called the 2D band) appears in Figure 1. A typical Raman spectrum of a graphitic material with four distinct bands is shown.

[0030] The presence of the G band is characteristic of an in-plane vibrational mode involving sp2 hybridized carbon. The D and D' bands are defect-induced Raman features and are not visible in highly crystalline carbon materials with few defects. The intensity ratio I for the D and G bands is D / I G is often used to characterize the amount of defects in graphitic materials.

[0031] However, in the framework of the present invention, we have considered another intensity ratio, namely the I between the D band and the D' band, as shown elsewhere in this specification. D / I D’ They found a surprising direct correlation between the amount of charge and battery performance.

[0032] The inventors D / I D’ However, the concentration of defects and the change in edge, vacancy-like, boundary-like defects, or carbon hybridization (e.g., sp 2 From sp 3 We believe that the variability in the variability of the variability is a good indicator of both the type of defects and the nature of the defects associated with the variability in the variability of the variability.

[0033] Ratio I D / I D’ A value greater than 4.0 is undesirable because it indicates that the concentration of defects in the carbon matrix material is too high, which may adversely affect, for example, the electronic conductivity of the composite particles. Furthermore, this indicates that defects are likely to cause sp 3 It could also be that it indicates the "more damaging" kind, such as those associated with hybridization.

[0034] Ratio I D / I D’A value lower than 0.9 is undesirable in any case, since it indicates that the concentration of defects in the carbon matrix is ​​too low, which may adversely affect, for example, the ionic conductivity of the composite particle.

[0035] In other words, the ratio I D / I D’ The technical effect associated with is greatest between 0.9 and 4.0.

[0036] In another embodiment according to the first aspect of the present invention, the ratio I D / I D’ is preferably at least 1.0, more preferably at least 1.2, even more preferably at least 1.4, particularly preferably at least 1.6, more particularly preferably at least 1.8, and most preferably at least 2.0. D / I D’ is preferably at most 3.8, more preferably at most 3.6, particularly preferably at most 3.4, more particularly preferably at most 3.2, and sufficiently preferably at most 3.0. In other words, the ratio I D / I D’ The technical effect associated with is greatest between 2.0 and 3.0.

[0037] In another embodiment according to the first aspect of the invention, the carbon matrix material is soft carbon, which corresponds to an arrangement of small, disordered graphitic domains that can be converted to graphite upon heating at temperatures above 3000°C, in contrast to hard carbon, which cannot be graphitized.

[0038] Soft carbon exhibits higher electronic conductivity than hard carbon and is therefore desirable. Furthermore, due to the disordered assembly of small graphite domains that results in the presence of nanovoids in the matrix material, the volume expansion of particles containing a matrix material that is predominantly soft carbon is reduced during anode lithiation compared to particles containing a matrix material that is predominantly graphite or graphene. The reduced volume expansion leads to longer battery cycle life.

[0039] In another embodiment according to the first aspect of the present invention, the composite powder has a silicon content S, expressed in weight percent (wt%), with 10wt%≦S≦60wt%, preferably 20wt%≦S≦50wt%.

[0040] Composite powders with a silicon content of less than 10 wt%, preferably less than 20 wt%, have too limited specific capacity and therefore cannot reach high battery energy density.Composite powders with a silicon content of more than 60 wt%, preferably more than 50 wt%, have too much volume expansion associated with this high silicon content, resulting in batteries with reduced cycle life.

[0041] In yet another embodiment according to the first aspect of the present invention, the composite powder has a carbon content C expressed in weight percent (wt%), where 30wt%≦C≦90wt%.

[0042] If the carbon content in the composite powder is less than 30 wt%, the carbonaceous matrix material is not present in an amount sufficient to completely coat the silicon-based particles, thus resulting in increased electrolyte decomposition on the surface of the silicon-based particles and thus increased SEI formation. If the carbon content in the composite powder is higher than 90 wt%, the specific capacity of the composite powder is too low.

[0043] In another embodiment according to the first aspect of the present invention, the composite powder has a silicon content S and an oxygen content N, both expressed in weight percent (wt%), where N≦0.20×S, preferably N≦0.15×S.

[0044] Composite powders with too high an oxygen content will suffer additional irreversible lithium consumption due to the formation of lithium silicates (Li2SiO3, Li4SiO4) during the initial lithiation of the powder, thereby increasing the initial irreversible capacity loss of batteries containing such composite powders.

[0045] In another embodiment according to the first aspect of the present invention, the silicon-based particles are characterized by a number-based particle size distribution having a d50 that is equal to or greater than 20 nm and equal to or less than 150 nm.

[0046] The number-based particle size distribution is based on a visual analysis (with or without the aid of an image analysis program) of the minimum number of silicon-based particles contained in the composite powder. This minimum number of silicon-based particles is at least 1000 particles. An example of the measurement of the number-based distribution of Si-based particles is given in the "Analytical Methods" section.

[0047] For clarity, for example, a d50 of 100 nm means that 50% of the number of at least 1000 silicon-based particles have a size smaller than 100 nm and 50% of the number of at least 1000 silicon-based particles have a size greater than 100 nm.

[0048] Silicon-based particles with a number-based particle size distribution having a d50 of less than 20 nm are very difficult to disperse efficiently in carbon matrix materials, which can reduce the electronic conductivity of the powder.

[0049] Silicon-based particles having a number-based particle size distribution with a d50 greater than 150 nm tend to break during their lithiation, causing a dramatic decrease in the cycle life of batteries containing such composite powders.

[0050] The d50 is considered to be unaffected by the process for making the composite powder, meaning that the d50 value of the silicon-based powder used as a precursor in the process is the same as the d50 value of the silicon-based particles contained in the composite powder.

[0051] In yet another embodiment according to the first aspect of the present invention, the silicon-based particles are coated with the carbon matrix material over at least 50% of their surface, preferably at least 75% of their surface. Preferably, the silicon-based particles are completely coated with the carbon matrix material. This can be visually confirmed based on analysis of one or more SEM images of a cross-section of a composite particle comprising the silicon-based particles.

[0052] As previously mentioned, a negative effect associated with silicon is that a thick SEI, i.e., a solid electrolyte interface, can form on the anode, especially on silicon-based particles. Because silicon-based particles undergo large volume changes during the lithiation / delithiation process in a battery, the already formed SEI can be destroyed again, resulting in continued lithium consumption and a significant decrease in the battery's cycle life. Protecting the surface of the silicon-based particles, at least partially, with a carbon matrix material is an effective solution to the continued formation of the SEI and the decrease in cycle life.

[0053] In another embodiment according to the first aspect of the present invention, the silicon content in the silicon-based particles is at least 80% by weight, preferably at least 90% by weight.

[0054] Preferably, the silicon-based particles do not contain elements other than Si and O, in order to avoid the silicon-based particles having an excessively low specific capacity. The silicon-based particles mainly contribute to the specific capacity of the composite powder, and it is preferable that their own capacity is as high as possible, and therefore the silicon content is as high as possible, in this case at least 80% by weight, preferably at least 90% by weight.

[0055] In another embodiment according to the first aspect of the present invention, the composite powder also contains graphite particles and / or graphene particles, such that neither the graphite particles nor the graphene particles are embedded in the carbon matrix material. By "neither the graphite particles nor the graphene particles are embedded in the carbon matrix material," we mean that less than 10% of the surface of the graphite particles and / or graphene particles is covered with the carbon matrix material, preferably less than 5% of the surface is covered with the carbon matrix material, and more preferably none of the surface is covered with the carbon matrix material. This can be visually confirmed based on the analysis of one or more SEM images of the cross section of the composite powder. Having the graphite particles and / or graphene particles not embedded in the matrix material has the advantage that only the silicon-based particles need to be covered with the carbon matrix material, thereby requiring less carbon matrix material, which results in a high irreversible capacity and a low specific capacity.

[0056] However, there may be some contacts between the composite particles and the graphite and / or graphene particles located on their outer surfaces, which is more preferred to ensure good electronic conductivity of the composite powder and therefore high rate capability of batteries containing the composite powder.

[0057] Furthermore, the graphite particles act as spacers between the composite particles, preventing them from clumping together into agglomerated powders. In the absence of such spacers, the agglomerated powders may require mechanical processing, such as a grinding process, for use in battery anodes, which may result in weakening of the integrity of the matrix material and ultimately lead to lower performance of batteries containing such agglomerated powders.

[0058] Alternatively, the composite powder may also contain exfoliated graphite, expanded graphite and / or graphene nanoplatelets, all of which are not embedded in a matrix material, for the same reasons as given above.

[0059] Since these graphitic materials may affect the Raman spectra of the composite powders, the ratio I for only the contribution of the carbon matrix material, especially the contribution to the D and D' bands, is D / I D’ These contributions must be removed to obtain , the procedure of which is explained in detail in the "Analysis Methods" section.

[0060] In yet another embodiment according to the first aspect of the present invention, the composite powder has a density of at most 10 m 2 / g, preferably at most 8m 2 / g BET surface area.

[0061] The composite powder preferably has a low BET specific surface area, which reduces the surface area of ​​the electrochemically active particles in contact with the electrolyte, thereby limiting the formation of a lithium-consuming SEI and, thereby, the degradation of the cycle life of batteries containing such composite powders.

[0062] In another embodiment according to the first aspect of the present invention, the composite particles have a volumetric particle size distribution with D10, D50 and D90, wherein 1 μm≦D10≦10 μm, 5 μm≦D50≦25 μm and 10 μm≦D90≦40 μm.

[0063] For clarity, for example, a D50 of 15 μm means herein that 50% by volume of the composite particles have a size smaller than 15 μm and 50% by volume of the composite particles have a size greater than 15 μm.

[0064] Particles of a matrix material having a volumetric particle size distribution with a D50 of less than 5 μm may have too high a specific surface area, which may result in an increased surface area for reaction with the electrolyte and for the formation of an SEI, which is disadvantageous for the reasons explained above.Particles of a matrix material having a volumetric particle size distribution with a D50 of more than 25 μm may be susceptible to breakage during lithium uptake due to their size, which may result in a shortened cycle life of a battery containing such particles.

[0065] In a second aspect, the present invention relates to a battery anode, preferably a cathode for a lithium-ion battery, comprising the composite powder according to the present invention. The anode typically also comprises an electronically conductive additive such as carbon black, graphite particles, graphene particles, carbon nanotubes, or a mixture thereof. The content of the electronically conductive additive is 0 to 10% by weight, particularly 0.1 to 5% by weight, based on the total weight of the anode layer (excluding the current collector).

[0066] The negative electrode typically also contains a binder or a mixture of binders. Specific examples of binders include polysaccharides, lithium polyacrylate (Li-PAA), sodium polyacrylate (Na-PAA), potassium polyacrylate (K-PAA), polyacrylic acid (H-PAA), sodium carboxymethyl cellulose (Na-CMC), and styrene-butadiene rubber (SBR). Binders are added to improve the cohesion of the various components of the negative electrode, mechanical strength on the current collector, or even flexibility. The binder accounts for 1% to 15% by weight, particularly 2% to 10% by weight, based on the total weight of the negative electrode layer (excluding the current collector). Examples of negative electrode formulations are described elsewhere herein.

[0067] Finally, the present invention also relates to a battery, preferably a lithium-ion battery, equipped with a negative electrode according to the invention and therefore containing a composite powder according to the invention as defined above or prepared as disclosed above.

[0068] More specifically, the battery according to the present invention comprises a negative electrode (anode), a positive electrode (cathode), and an electrolyte, preferably a non-aqueous electrolyte. Examples of the positive electrode include LiCoO2, LiNi 0,6 Mn 0,2 Co 0,2 O2, LiNi 0,8 Mn 0,1 Co 0,1 O2, LiNi 0,8 Co 0,15 Al 0,05 O2, Li 1,2 Ni 0,2 Mn 0,6Examples of the positive electrode active material include 02, LiFePO4, and the like. The electrolyte can be preferably a non-aqueous electrolyte, a non-aqueous polymer electrolyte, or even a solid electrolyte. Specific examples include organic electrolytes obtained by dissolving lithium salts such as LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, CH3SO3Li, and CF3SO3Li in non-aqueous solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butylene carbonate, acetonitrile, propionitrile, dimethoxyethane, tetrahydrofuran, and γ-butyrolactone; gel polymer electrolytes including polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, and polymethyl methacrylate; and solid polymer electrolytes including polymers with ethylene oxide bonds. The electrolyte may contain an additive that undergoes a decomposition reaction during initial charging of the lithium-ion battery. Specific examples of the additive include vinylene carbonate (VC), biphenyl, propane sultone (PS), fluoroethylene carbonate (FEC), and ethylene sultone (ES). The amount of the additive is preferably 0.1 wt % or more and 20 wt % or less of the total weight of the electrolyte.

[0069] [Brief description of the drawing] FIG. 1 is a diagram showing the Raman spectrum of a graphite material. [Figure 2] Raman spectrum of composite powder E1 using peak fitting.

[0070] Analytical methods used Silicon content measurement The silicon content of the composite powders is measured by X-ray fluorescence (XRF) using an energy dispersive spectrometer. This method has a random experimental error of ±0.3 wt% Si.

[0071] Oxygen content measurement The oxygen content of composite powders is determined using a LECO TC600 oxygen / nitrogen analyzer in the following manner: A sample of the powder to be analyzed is placed in a closed tin capsule, which is itself placed in a nickel basket. The basket is placed in a graphite crucible and heated to over 2000°C under helium as carrier gas. This melts the sample, and oxygen reacts with the graphite from the crucible until it becomes CO or CO2 gas. These gases are directed into an infrared measuring cell. The observed signal is recalculated into the oxygen content.

[0072] Determination of carbon content The carbon content of composite powders is measured using a Leco CS230 carbon-sulfur analyzer in the following manner: The sample is melted in a ceramic crucible in a high-frequency furnace with a constant flow of oxygen. The carbon in the sample reacts with the oxygen gas and leaves the crucible as CO or CO2. After finally converting any CO present to CO2, all the CO2 produced is finally detected by an infrared detector. The signal is finally converted to carbon content.

[0073] Determination of specific surface area (BET) The specific surface area of ​​the composite powder was measured by the Brunauer-Emmett-Teller (BET) method using a Micromeritics Tristar 3000. First, 2 g of the powder to be analyzed was dried in an oven at 120 °C for 2 hours, followed by a N2 purge. Then, to remove adsorbed species, the powder was degassed under vacuum at 120 °C for 1 hour prior to measurement.

[0074] Electrochemical performance determination The electrochemical performance of the composite powders in the examples and comparative examples is determined by the following method.

[0075] The powder to be evaluated is sieved using a 45 μm sieve and mixed with carbon black, carbon fiber, and sodium carboxymethyl cellulose binder (2.5 wt%) in water. The ratio used is 89 parts composite powder / 1 part carbon black (C65) / 2 parts carbon fiber (VGCF) and 8 parts carboxymethyl cellulose (CMC). These components are mixed in a Pulverisette 7 planetary ball mill at 250 rpm for 30 minutes.

[0076] Copper foil washed with ethanol is used as a current collector. A 200 μm thick layer of the mixed components is coated onto the copper foil. The coated copper foil is then dried in a vacuum at 70 °C for 45 minutes. A 1.27 cm thick layer is removed from the coated and dried copper foil. 2 Disks were punched and used as electrodes in coin cells using lithium metal as the counter electrode. The electrolyte was 1 M Li PF6 dissolved in EC / DEC 1 / 1 + 2% VC + 10% FEC solvent.

[0077] All coin cells were cycled using a high-precision battery tester (Maccor4000 series) according to the following procedure, where "CC" stands for "constant current" and "CV" stands for "constant voltage."

[0078] ● Cycle 1: ○ 6-hour break CC lithiation up to 10mV at C / 10, then CV lithiation up to C / 100 ○ 5 minute break ○ CC delithiation up to 1.5V at C / 10 ○ 5 minute break ● Cycle 2 and beyond: CC lithiation to 10mV at C / 2, then CV lithiation to C / 50 ○ 5 minute break ○ CC delithiation up to 1.2V at C / 2 ○ 5 minute break

[0079] The Coulombic Efficiency (CE) of a coin cell is the ratio of the capacity upon delithiation to the capacity upon lithiation in a given cycle, calculated for the initial cycle and subsequent cycles. The initial cycle is the most important in terms of Coulombic Efficiency, since the SEI formation reaction has a significant impact on CE. Typically, for silicon-based powders, the Coulombic Efficiency in the initial cycle can be as low as 80% (or even lower), which corresponds to an irreversible capacity loss of 20% of the coin cell, which is very significant. The goal is to achieve a CE of at least 90% in the initial cycle.

[0080] Even if the CE rises substantially over subsequent cycles, typically above 99%, those skilled in the art will recognize that even small differences in coulombic efficiency per cycle can have a significant cumulative effect over the hundreds or thousands of charge-discharge cycles that a battery is expected to last. As an example, a cell with an initial capacity of 1 Ah and an average CE of 99.8% will have a remaining capacity of 0.8 Ah after 100 charge-discharge cycles, which is 60% higher than a cell with an average CE of 99.5% (0.5 Ah).

[0081] The target for the average CE from cycle 5 to cycle 50 is to reach at least 99.5%, preferably at least 99.55%, for cells containing composite powders with a specific capacity of 800±20 mAh / g.

[0082] Determination of numerical particle size distribution The number-based particle size distribution of the silicon-based particles is determined by electron microscopy (SEM or TEM) of cross-sections of the composite powders, combined with image analysis.

[0083] To do this, a cross-section of a composite powder comprising multiple cross-sections of composite particles, each of which comprises multiple cross-sections of silicon-based particles, is prepared according to the procedure detailed below.

[0084] 500 mg of the composite powder to be analyzed was embedded in 7 g of resin (Buehler EpoxiCure 2) consisting of a mixture of 4 parts epoxy resin (20-3430-128) and 1 part epoxy hardener (20-3432-032). The resulting 1-inch diameter sample was allowed to dry for at least 8 hours. It was then first mechanically polished using a Struers Tegramin-30 to reach a maximum thickness of 5 mm, and then further polished by ion beam polishing (Jeol SM-09010 Cross Section Polisher) at 6 kV for approximately 6 hours to obtain a polished surface. Finally, a carbon coating was applied to this polished surface by carbon sputtering for 12 seconds using a Cressington 208 carbon coater to obtain the sample, also known as a "cross section," that was analyzed by SEM.

[0085] The prepared cross section was then scanned using a Bruker EDS detector Xflash5030-127 (30 mm 2 The analysis is carried out using a JEOL FEG-SEM JSM-7600F equipped with a 127 eV (127 eV) detector. The signal from this detector is processed by a Bruker Quantax 800 EDS system.

[0086] A voltage of 15 kV is applied at a working distance of a few millimeters to generate a magnified image. When pricing optical microscope images, images of backscattered electrons are reported.

[0087] The size of a silicon-based particle is considered to correspond to the maximum linear distance between two points on the periphery of an individual cross-section of that silicon-based particle.

[0088] To illustrate, but not limit, the measurement of the number-based particle size distribution of silicon-based particles, an SEM procedure is provided below. 1. Obtain multiple SEM images of the cross section of a composite powder containing composite particles with dispersed silicon-based particles. 2. Adjust the image contrast and brightness settings to easily visualize the cross-sections of the composite particles and silicon-based particles. Due to their different chemical compositions, both particle types can be easily distinguished by the difference in brightness. 3. Using suitable image analysis software, select at least 1000 individual cross-sections of silicon-based particles from the acquired SEM image(s) that do not overlap with another cross-section of the silicon-based particle. These individual cross-sections of silicon-based particles can be selected from one or more cross-sections of a composite powder comprising composite particles and silicon-based particles. 4. For each of the at least 1000 individual cross-sections of the silicon-based particle, measure the size of the individual cross-section of the silicon-based particle using suitable image analysis software.

[0089] Next, the d10, d50, and d90 values ​​of the number-based particle size distribution of the silicon-based particles determined using the above method are calculated. These number-based particle size distributions can be easily converted to weight-based or volume-based particle size distributions using well-known mathematical formulas.

[0090] Measurement of volumetric particle size distribution The volumetric particle size distribution of the composite particles is measured using a laser diffraction particle size analyzer, Malvern Mastersizer 2000. The following measurement conditions are selected: Compression range, active beam length 2.4 mm, measurement range: 300 RF, 0.01 to 900 μm. Sample preparation and measurements are carried out according to the manufacturer's instructions.

[0091] Raman spectroscopy Raman spectroscopy of the composite powder is carried out using a Renishaw inVia Qontor Raman spectrometer using 532 nm laser excitation.

[0092] To process the acquired spectra, the following steps are performed. 1. Subtract the background by removing both the cosmic ray and baseline contributions. 2. Using appropriate software, the obtained spectrum is fitted to three curves for the D, G, and D' bands, as shown in Figure 2. If graphite particles are present, the spectrum of pure graphite is first obtained and the contribution of the composite powder to the spectrum is subtracted. If graphite particles are not present, all of the D, G, and D' bands are necessarily contributions from the carbon matrix. 3. Measure the ID / ID' ratio.

[0093] Experimental Preparation of Examples Comparative Example 1 (CE1) not according to the invention To prepare the powder of Comparative Example 1, a 60 kW radio frequency (RF) inductively coupled plasma (ICP) was applied, using argon as the plasma gas, into which micron-sized silicon powder precursor was injected at a rate of about 200 g / h, resulting in a prevailing temperature (i.e., in the reaction zone) of over 2000 K. In this first process step, the precursor was completely vaporized. In the second process step, a 20 Nm argon gas was added to reduce the gas temperature to below 1600 K. 3 An argon flow of 10000000 / hr is used as a quench gas immediately downstream of the reaction zone to nucleate metallic submicron silicon powder. Finally, a passivation step is carried out at a temperature of 100°C for 5 minutes by adding 100 L / hr of a N2 / O2 mixture containing 1 mol% oxygen.

[0094] The specific surface area (BET) of the obtained silicon powder was measured and found to be 82 m 2 / g. The oxygen content of the obtained silicon powder is measured to be 7.9 wt %. The number-based particle size distribution of the silicon powder is measured to be d10=52 nm, d50=111 nm, and d90=171 nm.

[0095] A dry blend is then made of 100 g of the resulting silicon powder and 840 g of polyvinyl chloride (PVC) with a melting point of 160° C. The blend is heated to a temperature of 190° C. under a nitrogen flow and, after a waiting period of 60 minutes, mixed under high shear for 30 minutes using a Cowles dissolver-type mixer operating at 1000 rpm.

[0096] The resulting mixture of silicon powder in PVC is cooled to room temperature and solidified, then crushed and sieved through a 400 mesh sieve to produce intermediate powder 1.

[0097] Next, 20 g of the resulting intermediate powder 1 was placed in a quartz crucible in a tubular furnace and heated to 900 °C at a heating rate of 3 °C / min. It was then held at that temperature for 2 hours and then cooled. All of this was done under an argon atmosphere. The resulting product contained dispersed silicon-based particles embedded in the soft carbon matrix formed by the thermal decomposition of PVC.

[0098] Finally, the calcined product is ball milled with alumina balls at 300 rpm for 1 hour, and sieved through a 325 mesh sieve to obtain the powder of Comparative Example 1.

[0099] The main synthesis parameters are summarized in Table 1.

[0100] The total Si content of this powder was measured by XRF to be 39.3 wt. % with an experimental error of ±0.3 wt. This corresponds to a calculated value based on a weight loss of about 84 wt. % of the PVC upon heating and a small weight loss of the other components upon heating. The calculated ratio of the carbon content resulting from carbonization of the PVC forming the matrix material to the silicon content in the powder is about 1.46. The oxygen content of this powder was measured to be 3.4 wt. The specific surface area (BET) of the resulting powder was measured to be 3.3 m 2 / g.

[0101] The volume-based particle size distribution of the obtained composite particles is D10 5.4 μm, D50 15.8 μm, and D90 24.6 μm.

[0102] The powder of Comparative Example 1 is then analyzed by Raman spectroscopy according to the procedure previously described. -1 The intensity of the D peak located at 1610 cm -1 A ratio of 0.54 to the intensity of the D' peak located at 0.54 is obtained. This value is reported in Table 2.

[0103] Example 1 (E1) according to the invention The composite powder of Example 1 (E1) is made using the same method as that for making the composite powder of Comparative Example 1 (CE1), except that Intermediate Powder 1 is heated to 1000°C instead of 900°C.

[0104] The total Si content of this composite powder was measured by XRF to be 39.3 wt%. The oxygen content of this powder was measured to be 3.5 wt%. The specific surface area (BET) of the resulting powder was measured to be 3.2 m 2 / g.

[0105] The volume-based particle size distribution of the obtained composite particles is D10 5.2 μm, D50 16.1 μm, and D90 25.2 μm.

[0106] The Raman spectrum obtained for composite powder E1 is shown in Figure 2. -1 The intensity of the D peak located at 1610 cm -1 A ratio of 1.23 to the intensity of the D' peak located at

[0107] Comparative Example 2 (CE2) not according to the invention To prepare the composite powder of Comparative Example 2 (CE2), the same silicon powder as in Comparative Example 1 (CE1) is used. A dry blend is prepared from 100 g of silicon powder and 750 g of polyvinyl chloride (PVC) with a melting point of 210° C. The blend is heated to a temperature of 240° C. under a nitrogen flow, and after a waiting period of 60 minutes, it is mixed under high shear for 30 minutes using a Cowles dissolver-type mixer operating at 1000 rpm.

[0108] The mixture of silicon powder in PVC thus obtained is cooled to room temperature and solidified, then crushed and sieved through a 400 mesh sieve to produce intermediate powder 2.

[0109] Next, 20 g of the resulting intermediate powder 2 was placed in a quartz crucible in a tubular furnace and heated to 900 °C at a heating rate of 3 °C / min, held at that temperature for 2 hours, and then cooled. All of this was done under an argon atmosphere. The resulting product contained dispersed silicon-based particles embedded in the soft carbon matrix formed by the thermal decomposition of PVC.

[0110] Finally, the calcined product is ball milled with alumina balls at 300 rpm for 1 hour, and sieved through a 325 mesh sieve to obtain the powder of Comparative Example 2.

[0111] The total Si content in this powder is measured to be 39.2 wt. %, which corresponds to a calculated value based on a weight loss of about 82 wt. % of the PVC upon heating and a small weight loss of the other components upon heating. The calculated ratio of the carbon content resulting from carbonization of the PVC in the powder to the silicon content is about 1.47. The oxygen content of this powder is measured to be 3.4 wt. %. The specific surface area (BET) of the resulting powder is measured to be 3.4 m 2 / g.

[0112] The volume-based particle size distribution of the obtained composite particles is D10 5.6 μm, D50 16.4 μm, and D90 25.6 μm.

[0113] Example 2 (E2) according to the invention The composite powder of Example 2 (E2) is made using the same method as that for making the composite powder of Comparative Example 2 (CE2), except that Intermediate Powder 2 is heated to 1000°C instead of 900°C.

[0114] The total Si content of this composite powder was measured by XRF to be 39.2 wt %. The oxygen content of this powder was measured to be 3.6 wt %. The specific surface area (BET) of the resulting powder was measured to be 3.5 m2 / g.

[0115] The volume-based particle size distribution of the obtained composite particles is D10 4.9 μm, D50 15.6 μm, and D90 23.8 μm.

[0116] Example 3 (E3) according to the invention To prepare the composite powder of Example 3 (E3), the same procedure as for the composite powder of Example 2 (E2) was used, except that 20 g of intermediate powder 2 was mixed with 26 g of graphite. The resulting mixture was then placed in a quartz crucible in a tubular furnace and heated to 1000°C at a heating rate of 3°C / min, held at that temperature for 2 hours, and then cooled. All of this was done under an argon atmosphere. In the resulting product, silicon-based particles were dispersed and embedded in the soft carbon matrix formed by the pyrolysis of PVC. The graphite particles were not embedded in the soft carbon matrix.

[0117] Finally, the calcined product is ball milled with alumina balls at 300 rpm for 1 hour and sieved through a 325 mesh sieve to obtain the powder of Example 3.

[0118] The ratio of the carbon content resulting from carbonization of PVC in composite powder E3 to the silicon content is about 1.47.

[0119] The total Si content of this composite powder was measured by XRF and found to be 17.0% by weight. The oxygen content of this powder was measured and found to be 1.5% by weight. The specific surface area (BET) of the resulting powder was measured and found to be 3.3 m 2 / g.

[0120] The volume-based particle size distribution of the obtained composite particles is D10 5.2 μm, D50 15.7 μm, and D90 24.4 μm.

[0121] Comparative Example 3 (CE3) not according to the invention To prepare the composite powder of Comparative Example 3 (CE3), the same silicon powder as that of Comparative Example 1 (CE1) is used. A wet blend is prepared from 100g of silicon powder and 180g of phenolic resin precursor (phenol + formaldehyde mixture) with a crosslinking temperature of 100°C, and mixed under high shear for 30 minutes in a Cowles dissolver mixer operating at 1000 rpm under nitrogen flow. The wet blend is heated to a temperature of 200°C for 30 minutes, still under nitrogen flow, to complete the polymerization reaction.

[0122] The mixture of silicon powder in phenolic resin thus obtained is cooled to room temperature and solidified, then crushed and sieved through a 400 mesh sieve to produce intermediate powder 3.

[0123] Next, 20 g of the resulting intermediate powder 3 was placed in a quartz crucible in a tubular furnace and heated to 1000°C at a heating rate of 3°C / min, held at that temperature for 2 hours, and then cooled. All of this was done in an argon atmosphere. Unlike the previously obtained composite powders, the composite powder of Comparative Example 3 has silicon-based particles dispersed and embedded in a hard carbon matrix formed by thermal decomposition of a phenolic resin.

[0124] Finally, the calcined product is ball milled with alumina balls at 300 rpm for 1 hour, and sieved through a 325 mesh sieve to obtain the powder of Comparative Example 1.

[0125] The total Si content in this powder is 39.2 wt. % as determined by XRF. This corresponds to a calculated value based on a weight loss of about 25 wt. % of the phenolic resin upon heating and a small weight loss of the other components upon heating. The calculated ratio of the carbon content to the silicon content resulting from carbonization of the phenolic resin in the powder is about 1.47. The oxygen content of this powder is measured to be 3.4 wt. %. The specific surface area (BET) of the resulting powder is measured to be 4.2 m 2 / g.

[0126] The volume-based particle size distribution of the obtained composite particles is D10 6.2 μm, D50 17.2 μm, and D90 26.3 μm. [Table 1]

[0127] Electrochemical evaluation of composite powders The prepared composite powders were tested in coin cells according to the procedure specified above. Only composite powder E3, which contains graphite, already achieved the target capacity of 800 mAh / g ± 20 mAh / g, while the others had specific capacities of approximately 1380 mAh / g. Therefore, composite powders E1, E2, CE1, CE2, and CE3 were mixed with graphite during electrode preparation, resulting in a capacity of approximately 800 mAh / g for the composite powder + graphite mixture. The results obtained for the average coulombic efficiency between cycle 5 and cycle 50 are shown in Table 2.

[0128] When comparing the results of the composite powders from E1 to E3 according to the present invention with the composite powders from CE1 to CE3, for the possible reasons mentioned above, the ratio I of 0.9 to 4.0, in particular 1.0 to 3.0, and even more particularly 1.0 to 2.6 is obtained. D / I D’ It can be seen that the best results are obtained with cells containing composite powders having [Table 2]

Claims

1. 1. A composite powder for use in a battery anode comprising composite particles, the composite particles comprising a carbon matrix material and silicon-based particles embedded in the carbon matrix material, the composite powder having a Raman spectrum with a D band and a D′ band both corresponding to contributions from the carbon matrix material and a Raman spectrum of 1330 cm －１ ~1360cm －１ I Ｄ and 1600 cm －１ ~1620cm －１ I Ｄ’ and the ratio I Ｄ / I Ｄ’ is at least 0.9 and at most 4.

0.

2. I Ｄ / I Ｄ’ 2. The composite powder of claim 1, wherein the ratio is at least 1.0 and at most 3.

0.

3. I Ｄ / I Ｄ’ 2. The composite powder of claim 1, wherein the ratio is at least 1.0 and at most 2.

6.

4. The composite powder according to any one of claims 1 to 3, wherein the carbon matrix material is soft carbon.

5. 5. Composite powder according to any one of claims 1 to 4, having a silicon content S, expressed in weight percent (wt%), with 10wt%≦S≦60wt%.

6. 6. Composite powder according to any one of claims 1 to 5, having a carbon content C expressed in weight percent (wt%), with 30wt%≦C≦90wt%.

7. 7. A composite powder according to any one of claims 1 to 6, having a silicon content S and an oxygen content N, both expressed in weight percent (wt%), with N≦0.20S.

8. 8. The composite powder of claim 1, wherein the silicon-based particles are characterized by a number-based particle size distribution having a d50, the d50 being equal to or greater than 20 nm and equal to or less than 150 nm.

9. 9. The composite powder according to claim 1, wherein the silicon-based particles are coated with the carbon matrix material over at least 50% of their surfaces.

10. 10. The composite powder according to claim 1, wherein the silicon-based particles have a silicon content of at least 80% by weight.

11. 11. The composite powder according to any one of claims 1 to 10, also comprising graphite particles and / or graphene particles, such that less than 10% of the surface of the graphite particles and / or graphene particles is coated with the carbon matrix material.

12. At most 10m ２ / g, preferably at most 8m ２ 12. The composite powder according to claim 1, having a BET surface area of ​​1 / g.

13. The composite powder according to any one of claims 1 to 12, wherein the composite particles have a volume-based particle size distribution having D10, D50, and D90, and wherein 1 µm ≦ D10 ≦ 10 µm, 5 µm ≦ D50 ≦ 25 µm, and 10 µm ≦ D90 ≦ 40 µm.

14. A negative electrode comprising the composite powder according to any one of claims 1 to 13.

15. A battery comprising the negative electrode of claim 14.

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