Silicon-based powders, electrodes and batteries containing such powders

Abstract

The present invention relates to silicon-based powders for use in battery negative electrodes. [Solution] A silicon-based powder for use in a battery negative electrode, the silicon-based powder comprising silicon-based particles having a number-based particle size distribution with a d50, where the particle size is considered to be the particle's largest dimension, and less than 8.0% of the particles have a size greater than two times the d50. Such silicon-based powders can be embedded in a matrix to form an active material powder. Preferably, d50<150 nm and d10>10 nm. The cycle efficiency of a battery negative electrode made using such powders is significantly improved.

Description

[Technical Field]

[0001] The present invention relates to powders, more particularly for use in battery electrodes, after or before further processing, and to electrodes and batteries containing such 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 have already penetrated and rapidly expanded into other industries, such as automotive and energy storage. The realizable advantage of such batteries is their high energy density combined with good power performance.

[0003] Li-ion batteries typically include several so-called Li-ion cells, which contain a positive electrode, also called a cathode, a negative electrode, also called an anode, and a separator, all immersed in an electrolyte. The Li-ion cells most frequently used in portable applications are developed using materials such as lithium cobalt oxide or lithium nickel manganese cobalt oxide for the cathode and natural or synthetic graphite for the anode.

[0004] It is known that one of the important limiting factors affecting the performance of batteries, especially the energy density of batteries, is the material involved in the electrochemical reaction in the anode. Therefore, in order to increase the energy density, new materials derived from, for example, tin, aluminum, and silicon have been investigated and developed in recent decades, and such developments are mostly based on the principle of alloying the materials with Li during Li incorporation during use.

[0005] The best candidate material appears to be silicon, since it can achieve a theoretical capacity of 3579 mAh / g (gravimetric), a capacity significantly greater than that of other candidate materials, as well as graphite (372 mAh / g).

[0006] However, one drawback of using silicon-based materials for the anode is their large volume expansion during charging, for example, as high as 300% when lithium ions are fully incorporated into the material by alloying or intercalation (a process often referred to as lithiation). The large volume expansion of silicon-based materials during Li incorporation can induce stresses in the silicon, which can lead to mechanical degradation of the silicon material.

[0007] The repeated mechanical degradation of silicon-based materials during the cycling of Li-ion batteries during charging and discharging can reduce the battery's lifespan to unacceptable levels.

[0008] In an attempt to mitigate the adverse effects of silicon volume change, many research studies have shown that reducing the size of silicon materials to submicron or nano-sized silicon particles and using these as negative electrode materials in electrochemical reactions may demonstrate a viable solution.

[0009] To accommodate the volume change, multiphase particles are usually used, in which silicon particles are mixed with a matrix material, usually a carbon-based material or a silicon-based alloy.

[0010] Another adverse effect of silicon is that a thick SEI (Solid-Electrolyte Interface) can form on the anode. The SEI is a complex reaction product of the electrolyte and lithium, and therefore reduces the availability of lithium for electrochemical reactions, resulting in poor cycling performance and loss of capacity per charge-discharge cycle. Furthermore, a thick SEI can increase the electrical resistance of the battery, thereby limiting the achievable charge and discharge rates.

[0011] In principle, SEI formation is a self-terminating process that stops as soon as a "passivation layer" forms on the silicon surface. However, due to the volume expansion of silicon, both the silicon and the SEI can be damaged during charging (lithiation) and discharging (delithiation), which can expose new silicon surfaces and initiate new SEI formation.

[0012] In the art, the lithiation / delithiation mechanism is commonly quantified by the so-called Coulombic efficiency, which is defined as the ratio of the energy removed from the battery during discharge to the energy used during charging (% per charge-discharge cycle). Therefore, most research on silicon-based anode materials has focused on improving the Coulombic efficiency.

[0013] The cumulative deviation from 100% coulombic efficiency over many cycles determines the useful life of the battery. Thus, simply put, an anode with a coulombic efficiency of 99.9% is twice as good as an anode with a coulombic efficiency of 99.8%. Summary of the Invention [Means for solving the problem]

[0014] The present invention relates to a silicon-based powder for use in a battery anode, the silicon-based powder comprising, and preferably consisting of, silicon-based particles having a number-based particle size distribution having a d50, the particle size of a particle being considered to be the largest linear dimension of the particle, and less than 8.0% of the total number of silicon-based particles having a particle size greater than two times the d50.

[0015] An advantage of the present invention is that it allows for the preparation of anodes with higher coulombic efficiencies.

[0016] Without being bound by theory, the inventors speculate that this may be related to the fact that larger particles are more susceptible to breakage due to mechanical stress during repeated expansion and contraction during use, thereby contributing disproportionately to the continued SEI formation. Therefore, the near absence of large particles, defined as larger than twice the average size, is beneficial.

[0017] Relatively narrow particle size distributions have been used up until now. For example, Korean Patent Publication No. 2015 / 0109056 discloses a narrow particle size distribution, particularly focusing on the absence of very fine particles but still having a significant fraction of relatively coarse particles. Also, European Patent No. 2966710 discloses a fine silicon powder with a d50 of 154 nm. In this powder, about 10% of the particles are greater than three times the d50 value, so this powder also has a significant coarse fraction. Also, European Patent No. 3133690 discloses a silicon powder with a relatively narrow particle size distribution, but without a particular focus on the coarse fraction.

[0018] Furthermore, lithium incorporation into larger particles, especially into their centers, is relatively slow because it is a diffusion-limited process. As a result, their near absence is also useful for improving capacity at high charge / discharge rates, since larger particles are suspected to be relevant in limiting the achievable charge / discharge rates.

[0019] To obtain the above-mentioned advantages to a greater extent, preferably, less than 6.0% of the total number of silicon-based particles have a particle size greater than twice the d50, more preferably, less than 5.0% of the total number of silicon-based particles have a particle size greater than twice the d50, even more preferably, less than 4% of the total number of silicon-based particles have a particle size greater than twice the d50, and even more preferably, less than 3.0% of the total number of silicon-based particles have a particle size greater than twice the d50.

[0020] In a preferred embodiment, less than 2% of the total number of silicon-based particles have a particle size greater than two times the d50.

[0021] Alternatively, the same invention may be defined as a silicon-based powder for use in a battery anode, the silicon-based powder comprising, and preferably consisting of, silicon-based particles having a number-based particle size distribution having a d50, the particle size of a particle being considered to be the largest linear dimension of the particle, and wherein less than 8.0% of the particles by number have a particle size greater than two times the d50, preferably less than 6.0% of the particles by number have a particle size greater than two times the d50, more preferably less than 5.0% of the particles by number have a particle size greater than two times the d50, even more preferably less than 4.0% of the particles by number have a particle size greater than two times the d50, even more preferably less than 3.0% of the particles by number have a particle size greater than two times the d50, and most preferably less than 2.0% of the particles by number have a particle size greater than two times the d50.

[0022] Alternatively, the same invention may be defined in another way as a silicon-based powder for use in a battery anode, the silicon-based powder comprising, and preferably consisting of, silicon-based particles, the silicon-based particles having a number-based particle size distribution having a d50, the particle size of a particle being considered to be the largest linear dimension of that particle, and the number of silicon-based particles having a particle size greater than two times the d50 divided by the total number of silicon-based particles is less than 0.080, preferably less than 0.060, more preferably less than 0.050, even more preferably less than 0.040, even more preferably less than 0.030, and most preferably less than 0.020.

[0023] The particle size distribution is preferably determined based on a total number of 500 or more particles.

[0024] Silicon-based particles can be observed by microscopy, particularly SEM and sometimes TEM, and their maximum linear dimension, in other words, their size as used herein, can be determined by automated image analysis. The maximum linear dimension of a particle is the largest measurable linear distance between two points on the periphery of the particle.

[0025] For clarity, it should be noted that the percentages mentioned relate to the number of particles greater than twice the d50 value, rather than the weight these particles represent. This is consistent with the use of a number-based size distribution, where dx represents x% of the total number of particles having a size less than or equal to d.

[0026] The silicon-based particles can have any shape, for example, substantially spherical, but can also have irregular shapes, rods, plates, and the like.

[0027] In a preferred embodiment, the particle size distribution has a d10 such that (d50-d10) / d50≦0.60, preferably (d50-d10) / d50≦0.50.

[0028] This limits the amount of very fine particles that are very easily highly oxidized during powder preparation and / or use, thereby increasing the oxygen content of the powder, which has a two-fold negative effect: first, the weight of the powder increases due to oxidation, resulting in an increase in the weight of the battery; and second, the oxidized silicon leads to irreversible consumption of lithium and therefore a high initial irreversible capacity.

[0029] In a preferred embodiment, the particle size distribution of the silicon-based particles has a d99 such that (d99-d50) / d50≦2.

[0030] In a preferred embodiment, the silicon-based powder has an oxygen content of greater than or equal to 1.5% by weight, at most 20% by weight, preferably at most 15% by weight.

[0031] As explained above, too much oxygen content can have a detrimental effect on the battery.

[0032] Too low an oxygen content can also have adverse effects.

[0033] SiO with x<2 xIt is well known that a layer of silicon carbide (SiC) naturally forms around silicon-based particles. The inventors have discovered that this layer protects against the formation of excess silicon carbide, SiC, during further processing when the silicon-based powder is embedded in a carbon-containing matrix material and treated at high temperatures to produce a practical active powder. Such SiC formation can prevent some of the silicon from participating electrochemically in the battery and can also form a diffusion barrier for lithium, thereby reducing the electrochemical performance of the silicon that is not converted to SiC.

[0034] To achieve this protective effect, SiO x There must be sufficient oxygen present in the form of

[0035] In a preferred embodiment, the silicon-based powder has an oxygen content of 2.5 wt. % or more, and in a more preferred embodiment, an oxygen content of 3.5 wt. % or more.

[0036] Preferably the particle size distribution has a d10>10 nm, preferably d10>20 nm.

[0037] For clarity, it is noted that silicon-based particles are typically nano-sized, having an average diameter d50 by number that is less than 150 nm.

[0038] In a preferred embodiment, the silicon-based particles have a chemical composition in which the sum of the silicon content, the oxygen content, and the carbon content is at least 95% by weight.

[0039] In a preferred embodiment, the silicon-based powder comprises at least 90% by weight, preferably at least 95% by weight, of said silicon-based particles.

[0040] In a preferred embodiment, the silicon-based particles have a chemical composition having at least 70% by weight silicon, preferably at least 80% by weight silicon.

[0041] For the avoidance of doubt, the following notes are made: The particle size of a particle is defined as the largest linear dimension of the particle. It will be apparent to those skilled in the art that, considering the overall size of the particle, this largest linear dimension is ideally determined by electron microscopy, which requires the particle to be embedded in a resin. Therefore, it will be apparent to those skilled in the art that the largest linear dimension of a particle is measured as the largest linear distance between two points around the particle when embedded in a resin, as observed by electron microscopy. It will be apparent to those skilled in the art that silicon-based powders have an oxygen content, which can be determined by any of a variety of methods that, when properly performed, will yield the same result. As those skilled in the art will appreciate, a common and widely used laboratory analysis is to determine the oxygen content by reducing the silicon-based powder with graphite and measuring the amount of CO and CO produced as a result of this reduction. It will be apparent to those skilled in the art that all powders, and powders according to the present invention, have a particle size distribution. It will also be apparent to those skilled in the art that such particle size distribution may be expressed as a number-based particle size distribution or a weight-based particle size distribution or many other types of particle size distribution, and that the sample size must be sufficiently representative, e.g., at least 500 particles for a number-based particle size distribution. It will be clear to those skilled in the art that in the field of particle technology, the critical size of a particle size distribution is usually referred to as dx, e.g. d10, d50 and d99, and that in the case of a number-based particle size distribution, dx represents the particle size at which x% of the total number of particles have a size less than or equal to dx.

[0042] The present invention further relates to an active material powder for use in a battery anode, the active material powder comprising particles of active material, the particles of active material comprising a matrix material and silicon-based particles, the silicon-based particles embedded in the matrix material, the silicon-based particles having a number-based particle size distribution having a d50, the particle size of the silicon-based particles being considered to be the largest linear dimension of the silicon-based particles, and less than 8.0% of the silicon-based particles have a particle size greater than two times the d50, preferably less than 6.0% of the silicon-based particles have a particle size greater than two times the d50.

[0043] In preferred embodiments of the active material powder, less than 4.0% of the silicon-based particles have a size greater than twice the d50, preferably less than 3.0% of the silicon-based particles have a size greater than twice the d50, and more preferably less than 2.0% of the silicon-based particles have a size greater than twice the d50.

[0044] In a preferred embodiment of the active material powder, the particle size distribution of the silicon-based particles has a d10 such that (d50-d10) / d50≦0.6, and preferably (d50-d10) / d50≦0.5.

[0045] In a preferred embodiment of the active material powder, the matrix material is a carbon-based matrix material, more preferably pitch or pyrolytic pitch.

[0046] In a preferred embodiment of the active material powder, the active material powder comprises at least 90% by weight, preferably at least 95% by weight, of said active material particles.

[0047] In a preferred embodiment of the powder, the oxygen content of the active material powder is at most 10% by weight, preferably at most 5% by weight, more preferably at most 4% by weight.

[0048] In a preferred embodiment of the active material powder, the d50 of the silicon-based particles is less than 150 nm, preferably less than 120 nm.

[0049] In a preferred embodiment of the active material powder, the particle size distribution of the silicon-based particles has a d10 that is >10 nm, and preferably, the d10 is >20 nm.

[0050] In a preferred embodiment of the active material powder, the active material powder comprises at least 20% by weight of the silicon-based powder, and at most 75% by weight of the silicon-based powder.

[0051] In a further preferred embodiment of the active material powder, the active material powder comprises at least 30% by weight of the silicon-based powder.

[0052] The very narrow particle size distribution of the silicon-based powder according to the present invention is important in this regard, because it enables better dispersion of the silicon-based powder in the matrix material than conventional silicon-based powders. As a result, the silicon-based powder according to the present invention allows the use of higher concentrations without having concentrated clusters of silicon-based particles that are inappropriately embedded inside the particles of the active material. Particles of the active material containing large clusters of silicon-based particles also swell more during lithiation than particles of the active material containing well-dispersed silicon-based particles having a narrow particle size distribution.

[0053] The reason for this is that, in contrast to powders having a broad particle size distribution, powders having a very narrow particle size distribution are less likely to form dense and strong aggregates before mixing with the matrix material, so that the disruption of the aggregates of silicon-based particles during mixing with the matrix material is much easier. `

[0054] It is widely recognized thermodynamically that substantially all of the oxygen present in the active material powder made of silicon-based particles embedded in a carbon-based matrix material is present in the oxide layer on the surface of the silicon-based particles. This enables the recalculation of the oxygen content of the silicon-based particles within the active material powder based on the total oxygen content of the active material powder.

[0055] This oxide layer is usually called the SiO x layer, and the average value of x is 0 < x < 2, but other atoms such as hydrogen, nitrogen, and carbon may also be included. Therefore, SiO x should be properly understood as a Si-rich and O-rich layer in which Si has an oxidation state higher than 0 and smaller than 4+ on average.

[0056] The present invention further relates to a negative electrode for a battery, the negative electrode comprising the silicon-based powder as defined above or the active material powder as defined above.

[0057] The present invention further relates to a battery comprising the silicon-based powder as defined above or the active material powder as defined above, preferably the battery having a negative electrode, the silicon-based powder or the active material powder being present in the negative electrode. DETAILED DESCRIPTION OF THE INVENTION

[0058] The present invention is further illustrated by the following counterexamples and examples.

[0059] Analytical methods used: Determination of oxygen content The oxygen content of the powders in the examples and comparative examples was measured using a Leco TC600 oxygen-nitrogen analyzer by the following method: A powder sample was placed in a closed tin capsule, which was then placed in a nickel basket. The basket was placed in a graphite crucible and heated to over 2000°C under helium as a carrier gas. This melted the sample, and the crucible allowed the oxygen to react with the graphite to form CO or CO gas. These gases were then introduced into an infrared measuring cell. The observed signal was recalculated to obtain the oxygen content.

[0060] Electrochemical performance determination The active material powder was sieved using a 45 μm sieve and mixed with carbon black, carbon fiber, and sodium carboxymethyl cellulose binder (2.5 wt%) in water in the ratio of 93 parts by weight of active material powder / 1 part by weight of carbon black / 2 parts by weight of carbon fiber and 4 parts by weight of carboxymethyl cellulose (CMC).

[0061] These ingredients were mixed in a Pulverisette 7 planetary ball mill at 250 rpm for 30 minutes.

[0062] Copper foil washed with ethanol was used as a current collector. A 200 μm thick layer of the mixed components was coated onto the copper foil. The coating was dried under vacuum at 70° C. for 45 minutes. A 1.27 cm thick layer was removed from the coated and dried copper foil. 2Disks were punched and used as electrodes in coin cells using lithium metal as the counter electrode. The electrolyte was 1 M LiPF6 dissolved in EC / DEC 1 / 1 + 2% VC + 10% FEC solvent. All samples were tested in a high-precision coin cell tester (Maccor 4000 series).

[0063] The coulombic efficiency of repeated charge-discharge cycles was determined at 0.5° C. The average coulombic efficiency of the cycles between the 5th and 50th cycles is reported.

[0064] Those skilled in the art will recognize that small differences in coulombic efficiency per cycle that occur over the hundreds or thousands of charge-discharge cycles that a battery is expected to last have a significant cumulative effect.

[0065] Particle size measurement The maximum size of the silicon particles was determined by SEM imaging by measuring the maximum measurable distance between two points on the periphery of the particle.

[0066] To be able to measure this, the powder was embedded in resin from which a cross section was taken.

[0067] Image analysis software was used to facilitate counting and sizing. At least 500 particles were measured per sample to obtain reliable data.

[0068] Subsequently, a particle size distribution based on number was determined from all measured particles in the sample.

[0069] Comparative Example 1 Not According to the Invention Silicon nanopowder was obtained by applying a 60 kW radio frequency (RF) inductively coupled plasma (ICP) using argon as the plasma gas, into which a micrometer-sized silicon powder precursor was injected at a rate of about 100 g / h, resulting in a prevailing temperature (i.e., in the reaction zone) of above 2000 K. In this first process step, the precursor was completely vaporized. In the second process step, a 10 Nm fumed gas was used to reduce the temperature of the gas to below 1600 K. 3 An argon flow of 1 / hr was used as a quench gas immediately downstream of the reaction zone to nucleate metallic submicron silicon powder. Finally, a passivation step was performed at a temperature of 100 °C for 5 min by adding 100 L / hr of a N2 / O2 mixture containing 1 mol% oxygen. The plasma gas flow rate was adjusted to obtain an average particle diameter d 50 is 106 nm, d 90 In this case, the plasma gas was 2.5 Nm. 3 / hour Ar was used.

[0070] The oxygen content was measured to be about 8.0% by weight.

[0071] To produce the active material powder, a blend of 16 g of the above silicon nanopowder and 32 g of petroleum-based pitch powder was made.

[0072] This was heated under N2 to 450°C so that the pitch melted and after a waiting period of 60 minutes, mixed under high shear for 30 minutes in a Cowles dissolver type mixer operating at 1000 rpm.

[0073] The resulting mixture of silicon nanopowder in pitch was cooled to room temperature under N2 and once solidified, was crushed and sieved through a 400 mesh sieve.

[0074] Synthetic battery grade graphite was added to the as-dried silicon nanopowder / pitch blend by dry mixing to obtain a silicon nanopowder / pitch / graphite mixture in the weight ratio of 1.0:2.0:7.6, respectively.

[0075] Ten grams of the resulting mixture was combusted in a quartz boat in a tube furnace heated to 1000°C at a heating rate of 3°C / min under a continuous flow of argon. The mixture was maintained at 1000°C for 2 hours. Heating was stopped, and the mixture was allowed to cool to room temperature under an argon atmosphere. The product was removed from the quartz vessel, ground in a coffee mill for 15 minutes, and sieved through a 400-mesh sieve.

[0076] The active material powder produced had a silicon content of 10% by weight.

[0077] Example 1 according to the present invention Micron-sized silicon powder precursor was injected at a rate of 50 g / h, and the quenching gas flow rate was set to 20 Nm 3 The same preparation method as in Comparative Example 1 was used, except that the time was 1 / hour.

[0078] The oxygen content of the resulting silicon nanopowder was tested and found to be 9.3% by weight.

[0079] The obtained silicon nanopowder was further used to form an active material powder in the same manner as in Comparative Example 1.

[0080] Examples 2 to 7 of the present invention The quenching gas flow rate is 15 Nm 3 / hour~20Nm 3 The same preparation method as in Example 1 was used, except that the injection rate was varied between 50 g / hr and 75 g / hr, and the micron-sized silicon powder precursor was injected at a rate of 50 g / hr to 75 g / hr, as shown in Table 1.

[0081] [Table 1]

[0082] The oxygen content of all the products in Examples 2 to 7 was measured and found to be in the range of 8.0% to 9.8% by weight.

[0083] The obtained silicon nanopowder was further used to form an active material powder in the same manner as in Example 1 and Comparative Example 1.

[0084] analysis The particle size distribution of the silicon nanopowder of the comparative example and the example was measured immediately before being incorporated into each active material powder. The results are shown in Table 2 below. The electrochemical performance of each active material powder was measured. The results are shown in Table 3 below.

[0085] [Table 2]

[0086] [Table 3]

[0087] A clear correlation between the proportion of particles greater than twice the d50 and electrochemical performance was observed, with silicon powders with a low proportion of particles greater than twice the d50 resulting in active material powders with superior performance.

[0088] Examples 8 to 13 of the present invention The same preparation method as in Example 1 was used, except that the passivation step was carried out at a temperature of 100 °C for 0.5 to 15 minutes by adding 100 L / h of an N2 / O2 mixture containing 0.1 to 1 mol% oxygen. As a result, the oxygen content of the powders varies as shown in Table 4 below.

[0089] All samples exhibited particle size distributions with d10, d50, d90, d95 and d99 values ​​comparable to those of Example 1.

[0090] The obtained silicon nanopowder was further used to form an active material powder in the same manner as in Example 1.

[0091] As shown in Table 4, the oxygen content of the silicon powder was reduced from 14.1 wt% in Example 8 to 1.6 wt% in Example 13 before being incorporated into the active material powder. The SiC content was measured by XRD spectroscopy. The XRD patterns were first fitted using the "Default Profile Fit" fitting function in the software (Plytical HighScore Plus). The main peak attributed to silicon (approximately 28.4° 2θ) was Cu 111) and the main peak due to SiC (about 35.7°2θ Cu The area of ​​the peak (111) was automatically calculated by the software, and the ratio of both peak areas (peak area SiC / peak area Si) was calculated. For all samples 1 to 8, values ​​between 1% and 10% were obtained.

[0092] The electrochemical performance was measured in the same manner as in Example 1 and resulted in high initial coulombic efficiency values ​​and maintained high average coulombic efficiency values, the latter indicating good cycle life as shown in the table.

[0093] Comparative Example 2 The same preparation method as in Example 1 was used, except that the passivation step was carried out at a temperature of 200 °C for 15 min by adding 100 L / h of a N2 / O2 mixture containing 1 mol% oxygen, resulting in an oxygen content of 23 wt%.

[0094] The resulting silicon nanopowder was further used to form an active material powder in the same manner as in Example 1. The SiC content in the final active material powder was measured and found to be below the detection limit of 0.5%.

[0095] Electrochemical testing showed a low first coulombic efficiency value of 82.0%, indicating a high loss of lithium during the first cycle.

[0096] Comparative Example 3 The same preparation method as in Example 1 was used, except that the passivation step was carried out at a temperature of 100 °C for 12 seconds by adding 100 L / h of a N2 / O2 mixture containing 0.1 mol% oxygen, resulting in an oxygen content of 1.0 wt%.

[0097] The resulting silicon nanopowder was further used to form an active material powder in the same manner as in Example 1. A significantly higher XRD peak ratio of SiC compared to 20% Si was measured.

[0098] A good first coulombic efficiency value of 88.0 was measured, and a reasonable average coulombic efficiency of 99.80% was observed, but a very low silicon capacity of about 2300 mAh / gSi was measured, which is significantly less than the theoretical value of 3579 mAh / gSi, with examples showing silicon capacities of 2900-3200 mAh / gSi.

[0099] [Table 4]

[0100] Examples 14 to 17 of the present invention The same preparation methods of silicon and active material powder were used as in Example 1. The silicon content in the active material powder was increased to 20 wt%, 30 wt%, 40 wt%, and 50 wt%, as shown in Table 5.

[0101] All samples exhibited oxygen content and silicon particle size distributions with d10, d50, d90, d95 and d99 values ​​comparable to Example 1.

[0102] The resulting silicon nanopowders were further used to form active material powders in the same manner as in Example 1. However, the silicon content was increased to 20 wt % (Example 14), 30 wt % (Example 15), 40 wt % (Example 16), and 50 wt % (Example 16), respectively.

[0103] Electrochemical performance was measured in coin cells similar to Example 1 and Comparative Example 1. However, to compare the results, the active material powder was diluted with graphite to bring the total silicon content in the coin cells to 10 wt %. As shown in Table 5, this resulted in excellent first coulombic efficiency values ​​of over 85% while maintaining good electrochemical average coulombic efficiency values.

[0104] Comparative Examples 4 and 5 Not According to the Invention The same silicon and active material powder preparation methods were used as in Example 2. The sample exhibited comparable oxygen content and silicon particle size distribution with d10, d50, d90, d95 and d99 values ​​to Comparative Example 2.

[0105] The resulting silicon nanopowder was further used to form active material powders in the same manner as in Example 1. However, the silicon content was increased to 40 wt % (Comparative Example 4) and 50 wt % (Comparative Example 5), respectively, as shown in Table 5 below.

[0106] The electrochemical performance was measured in coin cells as in Example 1 and Comparative Example 1. However, to compare the results, the active material powder was diluted with graphite to bring the total silicon content in the coin cells to 10 wt %.

[0107] As shown in Table 5, this resulted in very low first coulombic efficiency values ​​of 81.1% and 80.2%.

[0108] [Table 5]

[0109] Examples 18-19 of the present invention The same silicon and active material powder preparation methods were used as in Example 1. Both samples exhibited similar oxygen content and silicon particle size distributions as Example 1, with d10, d50, d90, d95, and d99 values.

[0110] The resulting silicon nanopowder was further used to form an active material powder in the following manner: The silicon powder was loaded into a 4-liter attritor along with a micron-sized FeSi2 iron-silicon alloy. Two separate experiments were performed using 25 wt% silicon nanopowder and 75 wt% FeSi2 (Example 18) and 40 wt% silicon nanopowder and 60 wt% FeSi2 (Example 19), respectively.

[0111] Note that because the silicon in FeSi2 is alloyed with iron, it does not have significant electrochemical activity. Instead, it is used solely as a matrix material for nano-sized silicon powder.

[0112] Both materials were milled with heptane as PCA at 85% loading at 84 rpm for 24 days in an inert argon atmosphere. After 24 days of milling, the product was cooled to room temperature. Finally, a passivation step was performed at 100 °C for 5 minutes by adding 100 L / h of a N2 / O2 mixture containing 1 mol% oxygen.

[0113] Electrochemical performance was measured in coin cells as in Examples 14 to 17. As shown in Table 6, this resulted in excellent first coulombic efficiency values ​​of 85% or greater, while maintaining good electrochemical average coulombic efficiency values.

[0114] [Table 6]

Claims

1. 1. A silicon-based powder for use in a battery anode, the silicon-based powder comprising silicon-based particles, the silicon-based particles having a number-based particle size distribution having a d50, the particle size of a particle being considered as the largest linear dimension of the particle, the silicon-based powder having an oxygen content of greater than or equal to 1.5 wt.% and less than 3.5 wt.%, or greater than 6.1 wt.% and less than or equal to 8.0 wt.%, and less than 8.0% by number of silicon-based particles have a particle size greater than two times the d50, and d50<150 nm; the maximum linear dimension of the particle is measured as the maximum linear distance between two points on the periphery of the particle when embedded in the resin when the embedded particle is observed by electron microscopy; the number-based particle size distribution is determined based on particle sizes of at least 500 particles; The particle size distribution by number has a d10, where d10 indicates that 10% of the total number of particles have a size equal to or less than d10; The number-based particle size distribution has a d50, where d50 indicates that 50% of the total number of particles have a size equal to or less than d50; The particle size distribution by number has a d99, where d99 indicates that 99% of the total number of particles have a size equal to or less than d99; The oxygen content is used to reduce the silicon-based powder with graphite and to reduce the CO and CO produced as a result of the reduction. ２ The silicon-based powder is determined by measuring the amount of

2. 2. The silicon-based powder of claim 1, wherein less than 4.0% of the total number of silicon-based particles have a particle size greater than two times the d50.

3. The silicon-based powder according to any one of claims 1 to 2, characterized in that the silicon-based powder has an oxygen content of 2.5% by weight or more.

4. The silicon-based powder according to any one of claims 1 to 3, characterized in that the particle size distribution of the silicon-based particles has a d99 such that (d99-d50) / d50≦2.

5. 5. The silicon-based powder according to claim 1, wherein the silicon-based particles have a chemical composition having at least 70% by weight of silicon.

6. 6. The silicon-based powder according to claim 1, characterized in that d50<120 nm.

7. 7. The silicon-based powder according to claim 1, wherein the particle size distribution has a d10 > 10 nm.

8. 8. An active material powder for use in a negative electrode of a battery, the active material powder comprising active material particles, the active material particles comprising a matrix material and the silicon-based powder according to any one of claims 1 to 7, the silicon-based powder being embedded in the matrix material.

9. 9. The active material powder according to claim 8, wherein the active material powder comprises at least 20% by weight of the silicon-based powder.

10. 10. The active material powder according to claim 9, wherein the active material powder comprises at most 75% by weight of the silicon-based powder.

11. 11. The active material powder according to claim 8, wherein the active material powder contains at least 90% by weight of the active material particles.

12. A negative electrode for a battery, the negative electrode comprising the silicon-based powder according to any one of claims 1 to 7, or the negative electrode comprising the active material powder according to any one of claims 8 to 11.

13. A battery comprising the silicon-based powder according to any one of claims 1 to 7 or the active material powder according to any one of claims 8 to 11.

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