Powder for use in the negative electrode of a battery, method for preparing such powder, and battery containing such powder

Abstract

The object of the present invention is to provide a stable, electrochemically active powder containing (i) particles, i.e., a matrix material and silicon-based subparticles embedded in the matrix material, and (ii) sulfur, which is advantageous in that it can achieve high capacity combined with a long cycle life, even when used once in the negative electrode of a Li-ion battery. [Solution] A powder suitable for use in the negative electrode of a battery, wherein the powder comprises particles, the particles comprising a matrix material and silicon-based subparticles embedded in the matrix material, the matrix material comprising a carbonaceous material, and the powder further comprising sulfur, wherein the weight content of sulfur in the powder is at least 0.1% of the weight content of the carbonaceous material in the powder and at most 1% of the weight content of the carbonaceous material in the powder.

Description

[Technical Field]

[0001] The present invention relates to a powder for use in the negative electrode of a battery, a method for preparing such a powder, and a battery containing such a powder. [Background technology]

[0002] Lithium-ion (Li-ion) batteries are currently the highest-performing batteries and have already become the standard for portable electronic devices. In addition, these batteries are already widespread and rapidly expanding in other industries such as automobiles and energy storage. The advantage of using such batteries lies in their high energy density combined with excellent power performance.

[0003] Li-ion batteries typically consist of several so-called Li-ion cells, each containing a positive electrode, also called a cathode, immersed in an electrolyte, a negative electrode, also called an anode, and a separator. Li-ion cells most frequently used for portable applications are developed using electrochemical active materials such as lithium cobalt oxide or lithium nickel manganese cobalt oxide for the positive electrode and natural or artificial graphite for the anode.

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

[0005] In this technical field, the performance of batteries containing silicon-based electrochemically active powders is generally quantified by the so-called full-cell cycle life, which is defined as the number of charge-discharge cycles or cycles that a cell containing such material can undergo until it reaches 80% 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 electrochemical active materials in the anode is their large volume expansion during charging. For example, when lithium ions are completely incorporated into the anode active material through alloying or insertion (a process often called lithiation), the volume expansion can reach up to 300%. This large volume expansion of the silicon-based material during lithium incorporation can induce stress in the silicon particles, which can gradually lead to mechanical degradation of the silicon-based material. This repeated mechanical degradation of the silicon-based electrochemical active material during the periodic charging and discharging of lithium-ion batteries can reduce the battery life to an unacceptable level.

[0007] Furthermore, a negative effect associated with silicon is the potential for the formation of a thick SEI, or solid electrolyte interface, on the anode. The SEI is a complex reaction product of the electrolyte and lithium, leading to a loss of lithium's availability for electrochemical reactions, resulting in poor cycle performance and consequently a loss of capacity per charge-discharge cycle. Moreover, a thick SEI can further increase the battery's electrical resistance, thereby limiting its ability to discharge and charge at high currents.

[0008] SEI formation is a self-terminating process based on the principle that it stops as soon as a "passivation layer" is formed on the surface of a silicon-based material. However, due to the volume expansion of silicon-based particles, both the silicon-based particles and the SEI may be damaged during discharge (lithiation) and recharging (delithiation), thereby releasing a new silicon surface and initiating new SEI formation.

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

[0010] Such composite powder is described, for example, in U.S. Patent No. 10,964,940, and is a particulate material composed of composite particles, wherein the composite particles include a porous carbon skeleton and a plurality of nanoscale elemental silicon domains located within the pores of the porous carbon skeleton. International Publication No. 2020 / 129879 discloses a negative electrode mixture for an all-solid-state lithium-ion battery including a negative electrode material and a solid electrolyte, and the negative electrode material includes a composite material (A) containing silicon-containing particles and a carbonaceous material, and one or more types of components (B) selected from a carbonaceous material and graphite.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] Despite the use of such composite powder, there is still room for improvement in the performance of batteries containing Si-based electrochemically active powder. In particular, existing composite powders cannot achieve both high capacity and long cycle life, which are essential for electric vehicle batteries.

[0013] (i) particles, i.e., particles including a matrix material and silicon-based sub-particles embedded in the matrix material, and (ii) sulfur-containing, stable electrochemically active powder, i.e., powder having high capacity combined with long cycle life, which has been used once in the negative electrode of a Li-ion battery, is advantageous in that it can achieve high capacity combined with long cycle life, which is an object of the present invention.

Means for Solving the Problems

[0014] This objective is achieved by providing the powder according to Embodiment 1, which, once used in the anode of a Li-ion battery, can achieve a higher initial coulombic efficiency (CE) and a higher average coulombic efficiency compared to Comparative Examples 1-5, as demonstrated in Examples 1-4.

[0015] The present invention relates to the following embodiments.

[0016] [Embodiment 1] In a first aspect, the present invention relates to a powder, wherein the powder comprises particles, the particles comprising a matrix material and silicon-based subparticles embedded in the matrix material, the matrix material comprising a carbonaceous material, and the powder further comprises sulfur, the weight content of sulfur in the powder being at least 0.1% of the weight content of the carbonaceous material and at most 1% of the weight content of the carbonaceous material.

[0017] Preferably, the weight content of sulfur in the powder is at most 0.8% by weight of the carbonaceous material, and more preferably, it is at most 0.6% by weight of the carbonaceous material.

[0018] Preferably, at least 50% by weight of the matrix material is a carbonaceous material, more preferably at least 70% by weight of the matrix material is a carbonaceous material, and most preferably at least 90% by weight of the matrix material is a carbonaceous material.

[0019] Preferably, the silicon-based subparticles are embedded in a carbonaceous material.

[0020] The statement "The particles consist of a matrix material and silicon-based subparticles embedded in the matrix material" means that the particles in the powder are larger on average than the silicon-based subparticles because they contain silicon-based subparticles. The particles are typically micrometer-sized, while the silicon-based subparticles are typically nanometer-sized.

[0021] "Silicon-based subparticles embedded in a matrix material" means that the silicon-based subparticles are fixed in the matrix material and surrounded by the matrix material. The majority of the silicon-based subparticles, preferably all of them, are covered by the matrix material. Therefore, in the powder according to Embodiment 1, the silicon-based subparticles are preferably only in contact with each other and / or only in contact with the matrix material.

[0022] Silicon-based subparticles can have any shape, for example, substantially spherical but irregular, rod-shaped, plate-shaped, etc. In silicon-based subparticles, silicon exists mostly as metal silicon, to which small amounts of other elements may be added to improve properties, or some impurities such as oxygen or trace amounts of metal may be present. Considering all elements other than oxygen, the average silicon content in such silicon-based subparticles is preferably 80% by weight or more, more preferably 90% by weight or more, based on the total weight of the silicon-based subparticles.

[0023] While not bound by theory, the inventors believe that the presence of sulfur in the powder enables the formation of crosslinks between small graphite domains of carbonaceous material contained in the matrix material, thereby increasing the elasticity of the carbonaceous material and, consequently, the elasticity of the matrix material. Thanks to its elastic properties, the matrix material can better prepare for the expansion / contraction of silicon-based subparticles during battery charging / discharging, thereby reducing the risk of matrix material fracture, i.e., the formation of additional solid electrolyte interfaces (SEIs), and consequently the risk of exposure of silicon-based subparticles to the electrolyte, which leads to a decrease in primary and average Coulomb efficiency.

[0024] If the sulfur content is too low, the desired technical effect of increasing the elasticity of the carbonaceous material from the matrix cannot be achieved; therefore, the weight content of sulfur in the powder should be 0.1% or more of the weight content of the carbonaceous material. Similarly, the weight content of sulfur in the powder should be 1% or less of the weight content of the carbonaceous material, preferably 0.8% or less, and more preferably 0.6% or less. If the sulfur content is too high, the carbonaceous material from the matrix becomes too elastic, and therefore excessive deformation occurs, especially during battery charging (i.e., lithiation of silicon-based subparticles). This can lead to unacceptable expansion of the negative electrode, and if the anode expands beyond what is permissible by the battery casing, it can cause both a shortened cycle life and safety problems. Furthermore, since sulfur is electrochemically inert, it is best to limit its content to the level necessary to obtain the technical effect in order to keep the specific capacity of the powder as high as possible.

[0025] The carbonaceous material content in the powder matrix material can be measured by conventional methods or calculated based on the specific volume of the powder. Examples of such calculations are provided in the "Analytical Methods" section.

[0026] Preferably, the powder also has a silicon content A and a carbon content B, both expressed in weight percent (wt%), where 10 wt% ≤ A ≤ 60 wt% and 30 wt% ≤ B ≤ 89 wt%. Too low a silicon content and / or too high a carbon content will result in a negative electrode material with too low specific capacity, which is undesirable for industrial applications. Too high a silicon content will result in excessive volume expansion during cycling, which is undesirable mainly for safety reasons. Too low a carbon content will be insufficient to completely coat the silicon-based subparticles, causing a reaction between the surface of the silicon-based subparticles and the electrolyte, resulting in the formation of an additional SEI layer and a decrease in battery performance.

[0027] [Embodiment 2] In the second embodiment according to Embodiment 1, the carbonaceous material includes graphite domains, and the graphite domains are 2θ of 26°~27°. Cu At maximum intensity I C According to the Scherrer equation applied to the X-ray diffraction peaks of the powder assigned to C(002) having the above characteristics, the average size is less than 10 nm.

[0028] Preferably, the graphite domains have an average size of less than 5 nm, more preferably less than 3 nm, and most preferably less than 2 nm. Graphite domains having an average size of less than 10 nm, preferably less than 5 nm, more preferably less than 3 nm, and most preferably less than 2 nm result in a powder with higher electronic conductivity compared to graphite domains having a size of 10 nm or more, and are therefore preferred. Furthermore, as already mentioned, the presence of sulfur in the powder causes the formation of crosslinks between the small graphite domains of the carbonaceous material contained in the matrix, thereby increasing the elasticity of the carbonaceous material and, therefore, the elasticity of the matrix material. Thus, the smaller the average size of the graphite domains of the carbonaceous material contained in the matrix, the more crosslinks are formed, the more elastic the matrix material becomes, and as already mentioned, this leads to an increase in the first Coulomb efficiency and the average Coulomb efficiency. In other words, there is a synergistic effect between sulfur and graphite domains having a size of less than 10 nm, preferably less than 5 nm, more preferably less than 3 nm, and even more preferably less than 2 nm.

[0029] The Scherrer equation (P. Scherrer, Gottinger Nachricheten 2,98(1918)) is a well-known equation for calculating the size of regular (crystalline) domains from X-ray diffraction data. Standardized samples may be used for calibration to avoid machine-to-machine variability.

[0030] The presence or absence of graphite domains in the matrix material and their average size can be determined, for example, by transmission electron microscopy (TEM) analysis. Examples of such analyses are provided in the "Analytical Methods" section.

[0031] [Embodiment 3] In the third embodiment according to Embodiment 1 or 2, the powder has a nitrogen adsorption / desorption ratio of 0.005 cm², as determined by nitrogen adsorption / desorption measurement. 3 It has a total specific volume of porosity lower than / g. Preferably, the powder has a density of 0.003 cm³. 3 It has a porosity lower than / g. More preferably, the powder is 0.002cm³. 3 It has a porosity lower than / g. Ideally, the powder is not porous at all.

[0032] High porosity is important for volumetric capacity (mAh / cm³). 3 It is advantageous to have powders with low porosity or non-porous properties, as this would lower the ratio (or Ah / I units) and contradict the objective of obtaining powders with high specific volume. Furthermore, the formation of crosslinks between small graphite domains of carbonaceous material contained in the matrix is ​​promoted when the matrix material is dense, i.e., when the matrix material and thus the powder have low porosity or are non-porous.

[0033] The porosity of a powder can be measured by nitrogen adsorption / desorption measurements. The fact that a powder is not porous can be confirmed by microscopic observation (using SEM or TEM) of one or more cross-sections of the powder particles. High-density particles should be considered non-porous, even if they contain a small amount of irregularly distributed pores (less than 10 per cross-sectional image at 50,000x magnification), as this is simply an undesirable result of the thermal decomposition of the carbon precursor used to form the matrix material.

[0034] [Embodiment 4] In a fourth embodiment according to Embodiment 1 or 2, the carbonaceous material is soft carbon. The matrix material may also consist of soft carbon. Soft carbon corresponds to an array of small, disordered graphite domains that can be converted to graphite when heated to a temperature of 3000°C, in contrast to hard carbon which cannot be graphitized.

[0035] Soft carbon exhibits higher electronic conductivity compared to hard carbon and is therefore desirable. Furthermore, thanks to the disordered aggregation of small graphite domains resulting in the presence of nanovoids in the matrix material, the volume expansion of particles containing a matrix material that is mostly soft carbon during anode lithiation is reduced compared to particles containing a matrix material that is mostly graphite or graphene.

[0036] [Embodiment 5] In a fifth embodiment according to any one of embodiments 1 to 4, at least 80% by weight of the sulfur contained in the powder is present in the matrix material, preferably at least 90% by weight of the sulfur contained in the powder is present in the matrix material.

[0037] In other words, less than 20% by weight, preferably less than 10% by weight, of the sulfur contained in the powder is located outside the matrix material. It is preferable that all of the sulfur contained in the powder be present in the matrix material, but it is not possible to exclude the migration of some of the sulfur to the silicon particles.

[0038] As explained earlier, the technical effect resulting from the presence of sulfur is an increased elasticity of the matrix material. Even if the technical effect can still be achieved with a reduced sulfur content, it is preferable that the majority of the sulfur, at least 80% by weight, preferably at least 90% by weight, be present in the matrix material. More specifically, the technical effect is expected to be fully maximized when the sulfur is present in the soft carbon contained in the matrix material.

[0039] [Embodiment 6] In a sixth embodiment according to any one of Embodiments 1 to 5, the silicon-based sub-particles have a number-based particle size distribution having a d NS 50, and the d NS 50 is 40 nm or more and 150 nm or less.

[0040] The number-based particle size distribution is based on a visual analysis, with or without the assistance of an image analysis program, regarding the minimum number of silicon-based sub-particles contained in the powder. This minimum number of silicon-based sub-particles is at least 1000 particles. Examples of the measurement of the number-based fraction of the particles are provided in the "Analysis Method" section.

[0041] For clarity, for example, a d NS 50 of 100 nm means that 50% of the number of at least 1000 silicon-based sub-particles have a size smaller than 100 nm, and 50% of the number of at least 1000 silicon-based sub-particles have a size larger than 100 nm.

[0042] Silicon-based sub-particles having a number-based particle size distribution having a d NS 50 of less than 40 nm are very difficult to disperse efficiently in the matrix material, which can reduce the electronic conductivity of the powder.

[0043] Silicon-based sub-particles having a number-based particle size distribution having a d NS 50 of more than 150 nm are prone to breakage during their lithiation, causing a dramatic shortening of the cycle life of a battery containing such a powder.

[0044] d NS 50 is considered not to be affected by the process for producing the powder, which means that the d NS 50 value of the silicon-based powder used as a precursor in the process is the same as the d NS 50 value of the silicon-based sub-particles contained in the powder.

[0045] [Embodiment 7] In the seventh embodiment, which follows any one of embodiments 1 to 6, the silicon-based subparticles have a silicon weight content of at least 80% by weight. Preferably, the silicon-based subparticles have a silicon weight content of at least 90% by weight. Preferably, the silicon-based subparticles do not contain elements other than Si and O in order to avoid a decrease in the specific volume of the silicon-based subparticles. The silicon-based subparticles mainly contribute to the specific volume of the powder, and it is preferable that their own volume be as high as possible, and therefore, the silicon content is as high as possible, in this case preferably at least 80% by weight, and preferably at least 90% by weight.

[0046] [Embodiment 8] In the eighth embodiment according to any one of embodiments 1 to 7, the powder has a silicon content A and an oxygen content C, both expressed in weight percent (W%), where C ≤ 0.3 × A, preferably C ≤ 0.2 × A, and more preferably C ≤ 0.1 × A.

[0047] If the oxygen content of the powder is too high, lithium oxide (Li2O) is formed during the initial lithiation of the powder, which negatively impacts the consumption of additional irreversible lithium, thereby increasing the initial irreversible capacity loss of batteries containing such powder.

[0048] [Embodiment 9] In the ninth embodiment, which follows any one of embodiments 1 to 8, the powder is at most 10 m 2 / g, preferably a maximum of 5m 2 It has a BET surface area of ​​ / g.

[0049] To limit the formation of lithium-consuming solid electrolyte interfaces (SEIs) and consequently limit the irreversible loss of capacity of batteries containing such powders, it is preferable to have a low BET specific surface area for the powder, thereby reducing the surface area of ​​electrochemically active particles that come into contact with the electrolyte.

[0050] [Embodiment 10] In a tenth embodiment following any one of embodiments 1 to 9, the powder further comprises graphite particles.

[0051] In particular, the graphite particles are not embedded in the matrix material. This can be visually confirmed by analyzing one or more SEM images of the powder's cross-section. The fact that the graphite particles are not embedded in the matrix material is beneficial for at least two reasons: (i) only the silicon-based subparticles need to be coated by the matrix material, and therefore, matrix materials with high irreversible capacity and low specific capacity are not very necessary; and (ii) particles containing matrix materials with silicon-based subparticles embedded within them are smaller than those in which the matrix material also contains graphite particles, which leads to suppression of volume expansion of the particles during lithiation during battery cycling.

[0052] However, some contact may exist between the two types of particles located on their outer surfaces. This is even more preferable in order to ensure good electronic conductivity of the powder and, therefore, a high rate capacity of the battery containing the powder.

[0053] Graphite particles act as spacers between particles containing a matrix material with silicon-based subparticles embedded within it, thus preventing these matrix material particles from agglomerating and transforming into agglomerated powder. Without such spacers, the agglomerated powder may require mechanical processing, such as grinding, for use in the negative electrode of a battery, which weakens the integrity of the matrix material and ultimately leads to lower performance in batteries containing such agglomerated powder.

[0054] The presence of graphite particles in the powder can be determined, for example, by X-ray diffraction analysis. This method is described in the "Analytical Methods" section.

[0055] Since graphene particles typically have a much higher specific surface area and are therefore expected to significantly increase the formation of the SEI layer during cycling, thereby degrading the performance of batteries containing such powders, especially in the initial cycles, it is preferable that the powder contains graphite particles and not graphene particles.

[0056] [Embodiment 11] In an eleventh embodiment, the present invention also relates to a method for preparing any of the powder variations defined above. The method includes the following steps:

[0057] In step A, a powder containing a carbon precursor, a powder containing silicon-based particles, and a powder containing sulfur are provided.

[0058] In step B, a powder containing a carbon precursor and a powder containing sulfur are mixed, and the resulting mixture is heated to a temperature higher than the softening point of the carbon precursor powder while the mixture is flowing, and maintained at that temperature. This ensures good dispersion of the sulfur powder within the flow of the carbon precursor.

[0059] In step C, a powder containing silicon-based particles is added to the mixture obtained in step B at a temperature still higher than the softening point of the powder containing the carbon precursor, under constant mixing conditions. This ensures good dispersion of the powder containing silicon-based particles within a flow that already contains the sulfur-containing powder.

[0060] In step D, the mixture obtained in step C is cooled to room temperature and then pulverized.

[0061] In step E, the powder obtained in step D is heat-treated at a temperature equal to at least 1000°C in an oxygen-free atmosphere. Examples of oxygen-free atmospheres include argon or nitrogen flow.

[0062] The additional step may include cooling the powder obtained in step E to room temperature, followed by final grinding and / or sieving.

[0063] Preferably, the powder containing silicon-based particles has a volume particle size distribution with a dvs50 value, where the dvs50 value is at most 200 nm. This is preferable for powders containing silicon-based particles that are easily dispersed during step C, and for powders obtained at the end of step E that contain uniformly distributed silicon-based subparticles.

[0064] [Embodiment 12] In the twelfth embodiment according to Embodiment 11, the mixture obtained in step B has a sulfur content equal to at least 0.06% by weight and at most 0.65% by weight. This is preferred to obtain the powder according to Embodiment 1.

[0065] [Embodiment 13] In the 13th embodiment according to Embodiment 11 or 12, the carbon precursor is converted to soft carbon during the heat treatment of step E. It is important that the temperature at which the heat treatment is performed is equal to at least 1000°C in order to completely convert the carbon precursor to soft carbon. The temperature at which the heat treatment is performed is preferably 1100°C or lower to prevent the possible formation of silicon carbide and the formation of graphite domains of carbonaceous material having an average size greater than 10 nm contained in the matrix.

[0066] [Embodiment 14] In a 14th embodiment according to any one of embodiments 11 to 13, the powder containing the carbon precursor is petroleum pitch. Petroleum pitch is advantageous in that it has a relatively high carbon yield of about 65% by weight when calcined. When calcined at a temperature of at least 1000°C, petroleum pitch is converted into soft carbon.

[0067] [Embodiment 15] In the 15th embodiment, the present invention ultimately relates to a battery comprising powder according to any one of embodiments 1 to 10. [Modes for carrying out the invention]

[0068] The following detailed description details preferred embodiments for realizing the implementation 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. In contrast, the present invention includes a number of substitutes, modifications and equivalents, as will become apparent when considering the modes for carrying out the invention described below.

[0069] [Analysis methods used] Measurement of Si content The Si content of the powders in the examples and comparative examples is measured by X-ray fluorescence (XRF) using an energy-dispersive spectrometer. This method has a stochastic experimental error of ±0.3 wt% Si.

[0070] When it is necessary to measure the silicon content of specific particles containing Si-based subparticles, or the silicon content of Si-based subparticles themselves, measuring silicon content by XRF can be difficult. In such cases, analysis using a scanning electron microscope (SEM-EDS) with energy-dispersive X-ray spectroscopy may be preferable. This makes it possible to measure the silicon content of a given particle or subparticle. To obtain an average silicon content value, it is sufficient to analyze 10 particles or subparticles.

[0071] Measurement of oxygen content The oxygen content of the powders in the examples and comparative examples is measured by the following method using an oxygen-nitrogen analyzer (Leco TC600): The powder sample for analysis is placed in a sealed tin capsule and then in a nickel basket. The basket is placed in a graphite crucible and heated to over 2000°C under helium as a carrier gas. This melts the sample, and the oxygen reacts with the graphite from the crucible until it becomes CO or CO2 gas. These gases are then introduced into an infrared measurement cell. The observed signal is recalculated as the oxygen content.

[0072] Determination of carbon content The carbon content of the powders in the examples and comparative examples is measured by the following method using a carbon-sulfur analyzer (Leco CS230): The sample is melted in a ceramic crucible in a high-frequency furnace under a constant oxygen flow. The carbon in the sample reacts with oxygen gas and is released from the crucible as CO or CO2. After the final conversion of the existing CO to CO2, all the generated CO2 is detected by an infrared detector. The resulting signal is finally converted into the carbon content.

[0073] Determination of sulfur content The sulfur content of the powders in the examples and comparative examples is measured by the following method using a carbon-sulfur analyzer (Leco CS230). Sulfur in the sample reacts with oxygen gas and is released from the crucible as SO2. All generated SO2 is detected by an infrared detector. The resulting signal is finally converted into the sulfur content.

[0074] Determination of specific surface area (BET) The specific surface area of ​​the powder is measured using the Brunauer-Emmett-Teller (BET) method with a Micromeritics Tristar 3000. First, 2 g of the powder to be analyzed is dried in an oven at 120°C for 2 hours, followed by an N2 purge. Then, prior to measurement, the powder is degassed under vacuum at 120°C for 1 hour to remove adsorbed species.

[0075] Determination of the total specific volume of porous material Using nitrogen adsorption / desorption analysis (Micromeritics Tristar 3020), the total specific volume of porosity of the powders in the examples and comparative examples is determined by the following method: The powder is introduced into a sample tube and prepared (heating, vacuum, or N2 gas flushing) to remove all foreign molecules from the powder surface and from the sample tube.

[0076] Next, it is cooled to the liquid N2 temperature at which N2 adsorption occurs on the powder particles. This adsorption occurs at a relative pressure (P / P) of 0.10 to 0.99. oIt is measured at a relative pressure of 0.99 to 0.10 (P / P). Subsequently, the relative pressure drops, and as a result, N2 desorption occurs on the powder particles. o ) is measured. In this way, the BJH pore size distribution curve is obtained. Finally, the total specific volume of the porous material is calculated.

[0077] Determination of electrochemical properties The electrochemical properties of the powders in the examples and comparative examples are measured by the following method.

[0078] The powder to be evaluated was sieved using a 45 μm sieve and mixed with carbon black, carbon fiber, and sodium carboxymethylcellulose binder (2.5 wt%) in water. The ratio used was 89 wts of the powder to be evaluated / 1 wt of carbon black (C65) / 2 wts of carbon fiber (VGCF) and 8 wts of carboxymethylcellulose (CMC). These components were mixed in a Pulverisette 7 planetary ball mill at 250 rpm for 30 minutes.

[0079] Copper foil cleaned with ethanol was used as the current collector. A 200 μm thick layer of the mixed components was coated onto the copper foil. The coated copper foil was then dried in a vacuum at 70°C for 45 minutes. 1.27 cm from the dried coated copper foil. 2 A circle was punched out and used as an electrode in a coin cell using lithium metal as the counter electrode. The electrolyte was 1M LiPF6 dissolved in EC / DEC 1 / 1 + 2%VC + 10%FEC solvent.

[0080] All coin cells are cycled using a high-precision battery tester (Maccor 4000 series) following the procedure outlined below. "CC" stands for "constant current" and "CV" stands for "constant voltage". ● Cycle 1: ○ 6-hour break ○ CC lithium conversion up to 10mV at C / 10, then CV lithium conversion up to C / 100. ○ 5-minute break ○ CC delithiation down to 1.5V with C / 10 ○ 5-minute break ● From Cycle 2 onwards: ○ CC lithium conversion up to 10mV at C / 2, then CV lithium conversion up to C / 50. ○ 5-minute break ○ CC delithiation down to 1.2V with C / 2 ○ 5-minute break

[0081] The Coulomb efficiency (CE) of a coin cell is the ratio of the delithiation volume to the lithiation volume in a given cycle, and is calculated for the initial cycle and subsequent cycles. The initial cycle is the most important from the perspective of Coulomb efficiency because the SEI formation reaction significantly affects CE. Typically, for silicon-based powders, the Coulomb efficiency in the initial cycle can be as low as 80% (or even lower), which represents a very large irreversible volume loss of 20% in the coin cell. The goal is to achieve at least 90% CE in the initial cycle.

[0082] In subsequent cycles, even if the CE typically rises well above 99%, a person skilled in the art will notice that even small differences in Coulomb efficiency per cycle have a significant cumulative effect over the hundreds or thousands of charge-discharge cycles that the battery is expected to sustain. For example, a cell with an initial capacity of 1Ah and an average CE of 99.8% will have a remaining capacity of 0.8Ah after 100 charge-discharge cycles, which is 60% higher than a cell with an average CE of 99.5% (a remaining capacity of 0.5Ah).

[0083] For a cell containing a negative electrode powder with a specific capacity of 840±20mAh / g, the goal is to achieve at least 90% Coulomb efficiency (CE) in the initial cycle, and at least 99.7% average CE in cycles 5 through 50.

[0084] Measurement of volume particle size distribution of powder The volume particle size distribution of the powder is determined using Laser Diffraction Sympatec (Sympatec-Helos / BFS-Magic 1812) according to the user manual. The following settings are used for measurement. Distributed system: Sympatec-Rodos-M Dispersion machine:Sympatec-Vibri 1227 Lens: R2 (range of 0.45 to 87.5 μm) Dispersion: 3 bar pressurized air Optical density: 3~12% Start / Stop: 2% Time axis: 100ms Supply rate: 80% Aperture: 1.0mm

[0085] Please note that the supply rate and aperture settings may change depending on the optical density.

[0086] Next, the volume particle size distribution of the powder containing silicon-based particles is determined using the method described above. VS 10, d VS 50 and d VS Calculate the 90 value.

[0087] Determination of particle size distribution based on number The number-based particle size distribution of silicon-based subparticles is determined by electron microscopy (SEM or TEM) analysis of the powder cross-section, combined with image analysis.

[0088] To do this, powder cross-sections containing multiple cross-sections of matrix material particles, each containing multiple cross-sections of silicon-based subparticles, are prepared according to the procedure detailed below.

[0089] 500 mg of the powder to be analyzed is embedded in 7 g of a resin (Buehler EpoxiCure 2) consisting of a mixture of 4 parts epoxy resin (20-3430-128) and 1 part epoxy curing agent (20-3432-032). The resulting 1-inch diameter sample is dried for at least 8 hours. It is then mechanically polished using a Struers Tegramin-30 to a maximum thickness of 5 mm, and then further polished by ion beam polishing (Cross Section Polisher Jeol SM-09010) at 6 kV for approximately 6 hours to obtain a polished surface. Finally, a carbon coating is applied to this polished surface by carbon sputtering using a Cressington 208 carbon coater for 12 seconds to obtain a sample, also called a "cross section," which will be analyzed by SEM.

[0090] Next, the prepared cross-section was examined using the Bruker EDS detector Xflash 5030-127 (30mm 2 The analysis is performed using a JEOL FEG-SEM JSM-7600F with a voltage of 127 eV. The signal from this detector is processed using a Bruker Quantax 800 EDS system.

[0091] By applying a voltage of 15kV at a working distance of several millimeters, a magnified image is generated. When assigning values ​​to images from an optical microscope, the image of backscattered electrons is reported.

[0092] The size of silicon-based subparticles is thought to correspond to the maximum straight-line distance between two points on the outer circumference of the individual cross-section of that particle.

[0093] To non-restrictively describe the measurement of the number-based particle size distribution of silicon-based subparticles, the procedure using SEM is shown below. 1. Obtain multiple SEM images of cross-sections of powder containing matrix material particles with dispersed silicon-based subparticles. 2. Adjust the image contrast and brightness settings to easily visualize the cross-sections of matrix material particles and silicon-based subparticles. Due to their different chemical compositions, the difference in brightness allows for easy distinction between particles and subparticles. 3. Using suitable image analysis software, select at least 1000 individual cross-sections of silicon-based subparticles from one or more acquired SEM images that do not overlap with other cross-sections of silicon-based subparticles. These individual cross-sections of silicon-based subparticles can be selected from one or more cross-sections of the powder containing the matrix material particles and the silicon-based subparticles. 4. For each of at least 1000 individual cross-sections of the silicon-based subparticle, the size of the individual cross-section of the silicon-based subparticle is measured using suitable image analysis software.

[0094] Next, the number-based particle size distribution of silicon-based subparticles determined using the above method is d NS 10, d NS 50 and d NS The 90 values ​​are calculated. These number-based particle size distributions can be easily converted to weight-based or volume-based particle size distributions using well-known formulas.

[0095] Measuring the size of graphite domains The size of the graphite domains contained in the carbonaceous material can be determined by TEM analysis of the cross-section of the powder obtained as described above.

[0096] However, the preferred method is X-ray diffraction (XRD) analysis of the powder. The following method is used.

[0097] Using CuKα1 and CuKα2 radiation, with λ=0.15418nm, step size 0.017° at 2θ, and scanning speed 34 minutes (2064 seconds), the ICDD database, PDF-4+ was used to identify this compound, at least approximately 2 cm². 3Measurements are taken on the surface of the powder material at 2θ angles from 5° to 90°, and XRD measurements of the powder are performed on the Panalytical'X Pert Pro system.

[0098] 2θ between 26° and 27° Cu The XRD peak with the maximum value corresponds to the (002) reflection of graphite carbon resulting from X-ray diffraction from the interplanar graphene layer. The background is first subtracted from the raw XRD data. Then, the 2θ values ​​at the half maximum intensity on the left and right sides of the C(002) peak are calculated. Cu Determine the value. The Full Width at Half Maximum (FWHM) value is obtained from these two 2θ values. Cu It is the difference in values. The FWHM value is usually measured using a program built into the X-ray diffractometer. Manual calculation can also be used.

[0099] The average size of the graphite domains is ultimately calculated by applying the Scherrer equation to the C(002) peak, using the precisely measured FWHM value, the instrument's X-ray wavelength, and the position of the C(002) peak.

[0100] Determination of the carbonaceous material content in the powder matrix material. If it is difficult to directly measure the carbonaceous material content in a powder matrix material using well-known physicochemical analytical techniques, the following mathematical methods can also be used to calculate this content.

[0101] Two powders will be used as examples for the application of this method. The first powder (Ex1) has the following content: 20.0 wt% silicon (Si), 1.6 wt% oxygen (O), 0.4 wt% sulfur (S), and 78 wt% carbon I, and has an average delithiation capacity of 795 mAh / g measured in the first cycle of three identical coin cells using the method described above. Carbonaceous materials containing Si-based particles and graphite domains with an average size of less than 10 nm are observed by TEM, and the average size of the domains is determined by applying the Scherrer equation as described above. Graphite particles or other materials with graphite domains larger than 10 nm are not observed.

[0102] The second powder (Ex2) has the following content: 20.0 wt% Si, 1.7 wt% O, 0.3 wt% S, and 78 wt% C, and has an average delithiation capacity of 820 mAh / g measured in the first cycle of three identical coin cells using the method described above. Both the Si-based particles and the carbonaceous material containing graphite domains with an average size of less than 10 nm, as well as the graphite particles not embedded in the matrix material, are observed by combining TEM and XRD analysis.

[0103] Carbonaceous materials with graphite domains smaller than 10 nm, and especially soft carbon, are typically known to have a specific capacity of approximately 250 mAh / g as a negative electrode material. Graphite particles are also known to have a capacity of approximately 350 mAh / g as a negative electrode material. For silicon, a specific capacity of 3000 mAh / g is used, taking into account the irreversible capacity loss that occurs during the first cycle.

[0104] Next, calculate the specific volume of the powder as follows: Specific capacity powder (mAh / g)=wt% Si×3000(mAh / g)+ wt% carbonaceous material × 250 (mAh / g) + wt% graphite × 350 (mAh / g) (Equation 1) wt% Si + wt% O + wt% S + wt% Carbonaceous material + wt% Graphite = 1 ⇔ wt% graphite = 1-wt% Si-wt% O-wt% S-wt% carbonaceous material (equation 2)

[0105] Substituting equation 2 into equation 1 yields equation 1 below: wt% carbonaceous material = (wt% Si×2650+(1-wt% O-wt% S)×350-specific capacity powder) / 100 (Formula 1)

[0106] Next, the graphite content can be calculated using equation 2.

[0107] Using equations 1 and 2, calculate the respective content of powders Ex1 and Ex2 and report it in Table 1.

[0108] [Table 1]

[0109] It can be noted that both powders Ex1 and Ex2 are powders according to the present invention.

[0110] This mathematical method was evaluated on 20 samples with known concentrations of different components and proved to have a precision margin of at least 10%.

[0111] Experimental preparation of comparative examples and examples [Example 1(E1) according to the present invention] To produce the powder of Example 1, a 60kW radio frequency (RF) inductively coupled plasma (ICP) was applied, using argon as the plasma gas. Micron-sized silicon powder precursor was injected into it at a rate of approximately 200 g / hour, bringing the silicon-based powder to a sufficient temperature (i.e., in the reaction zone) of over 2000K. In this first process step, the precursor was completely vaporized. In the second process step, 20 Nm was added to lower the gas temperature to below 1600K.3 A stream of argon at 1 / hour 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 100°C for 5 minutes by adding an N2 / O2 mixture containing 1 mol% oxygen at a rate of 100 L / hour.

[0112] The specific surface area (BET) of the obtained silicon powder was measured to be 81 m². 2 The value is / g. The oxygen content of the obtained silicon powder was measured to be 7.8% by weight. The particle size distribution based on the number of silicon particles was measured to be d NS 10 = 59 nm, d NS 50 = 114 nm and d NS 90 = 192 nm.

[0113] Next, a dry blend was prepared from 200 g of petroleum-based pitch powder and 0.25 g of sulfur powder (Sigma-Aldrich, 99.98% purity). It should be noted that the sulfur content of the petroleum-based pitch powder used here was measured using the method described above and was below the detection limit of the instrument. Therefore, the contribution of the pitch powder to the sulfur content in the final powder is negligible.

[0114] The blend is heated to a temperature of 400°C under a nitrogen stream, and after a 60-minute waiting period, it is mixed for 30 minutes under high shear using a Cowles melter mixer operating at 1000 rpm.

[0115] Next, 100 g of silicon powder is added to the freshly obtained mixture, still at 400°C. The blend is heated to a temperature of 400°C under a nitrogen stream, and after a 60-minute waiting period, it is mixed for 30 minutes under high shear using a Cowles dissolving mixer operating at 1000 rpm.

[0116] The mixture of silicon-based powders obtained in this way is cooled to room temperature, solidified, pulverized, and sieved through a 400-mesh sieve to produce an intermediate powder.

[0117] The intermediate powder is subjected to further heat treatment as follows: the product is placed in a quartz crucible in a tubular furnace and heated to 1020°C at a heating rate of 3°C / min, held at that temperature for 2 hours, and then cooled. All of this is done under an argon atmosphere.

[0118] The calcined product is then manually ground in a mortar and pestle, and sieved through a 325-mesh sieve to form the final powder.

[0119] The total Si content of this powder, as measured by XRF, is 40.1% by weight. The oxygen, carbon, and sulfur content of this powder is 3.4% by weight, 56.4% by weight, and 0.109% by weight, respectively. Since all the carbon is in the matrix material and corresponds to soft carbon with graphite domains of less than 10 nm, the ratio "S / carbonaceous material in matrix" is equal to 0.193%.

[0120] The specific surface area (BET) of the obtained powder was measured to be 4.8 m². 2 It is / g.

[0121] The main physicochemical properties of powder E1 are reported in Table 2.

[0122] [Examples 2(E2) and 3(E3) of the present invention] To produce the powders of Example 2 (E2) and Example 3 (E3), the same method as for the powder of Example 1 was used, except that 0.45 g and 0.7 g of sulfur powder were used instead of 0.25 g in Example 1. The main physicochemical properties of the resulting powders E2 and E3 are reported in Table 2.

[0123] [Comparative Example 1 (CE1) not based on the present invention] To produce the powder of Comparative Example 1 (CE1), the same method as for the powder of Example 1 was used, except that sulfur powder was not used. The main physicochemical properties of the resulting powder CE1 are reported in Table 2.

[0124] [Comparative Example 2 (CE2) not based on the present invention] To produce the powder of Comparative Example 2 (CE2), the same method as for the powder of Example 1 was used, except that 0.1 g of sulfur powder was used instead of 0.25 g as in Example 1. The main physicochemical properties of the resulting powder CE2 are reported in Table 2.

[0125] [Comparative Example 3 (CE3) Not Based on the Invention] To produce the powder of Comparative Example 3 (CE3), the same method as for the powder of Example 1 was used, except that 1.7 g of sulfur powder was used instead of 0.25 g as in Example 1. The main physicochemical properties of the resulting powder CE3 are reported in Table 2.

[0126] [Comparative Example 4 (CE4) not based on the present invention] To produce the powder of Comparative Example 4 (CE4), the same method as for the powder of Example 3 was used, except that the further heat post-treatment applied to the intermediate powder was carried out at 1200°C for 8 hours instead of 1020°C for 2 hours for the powder of Example 3. The main result of this heat post-treatment, performed at a higher temperature and for a longer time, is that the average size of the graphite domains of the carbonaceous material contained in the matrix of powder CE4 is 14 nm, whereas all other powders produced at a temperature of 1020°C, in particular powder E3, are less than 10 nm. The main physicochemical properties of the resulting powder CE4 are reported in Table 2.

[0127] [Comparative Example 5 (CE5) not based on the present invention] To produce the powder of Comparative Example 5 (CE5), a blend was prepared from 100 g of the silicon-based powder produced in Example 1 and a thermosetting polymer. The weight ratio of the thermosetting polymer to Si was 0.2. The polymer used was a phenol-formaldehyde resin. The blend was then placed in an aerated oven to cure the thermosetting polymer at a temperature of 150°C. The resulting cured powder was then bead-milled to submicron particles.

[0128] Next, a dry blend is prepared from 180 g of petroleum-based pitch powder and 0.7 g of sulfur powder. This blend is heated to 400°C under a nitrogen stream, and after a 60-minute waiting period, it is mixed for 30 minutes under high shear using a Cowles dissolving mixer operating at 1000 rpm. Then, 100 g of pulverized silicon polymer particles are added to the freshly obtained mixture, still at 400°C. This blend is heated to 400°C under a nitrogen stream, and after a 60-minute waiting period, it is mixed for 30 minutes under high shear using a Cowles dissolving mixer operating at 1000 rpm.

[0129] The mixture of silicon polymer particles in the pitch obtained in this way is cooled to room temperature, solidified, pulverized, and sieved through a 400-mesh sieve to produce an intermediate powder.

[0130] This intermediate powder is subjected to further post-heat treatment as follows: the product is placed in a quartz crucible in a tubular furnace and heated to 1020°C at a heating rate of 3°C / min, held at that temperature for 2 hours, and then cooled. All of this is done under an argon atmosphere. The thermosetting polymers present in the mixture decompose without actually undergoing a melting process, leaving pores in the carbon matrix created during the heat treatment. The thermosetting polymers act as sacrificial materials to create porosity.

[0131] The calcined product is then manually ground in a mortar and pestle, and sieved through a 325-mesh sieve to form the final powder.

[0132] The total Si content in this powder, as measured by XRF, is 40.1% by weight. The oxygen, carbon, and sulfur content in this powder, as measured, is 3.4% by weight, 56.2% by weight, and 0.305% by weight, respectively. The total specific volume of the porous material is 0.016 cm³. 3 While equal to / g, the total specific volume of the porous material of all powders E1-E3 and C1-CE4 is 0.002 cm³. 3 / g~0.004cm 3The composition is as follows: The matrix material observed by SEM microscopy of several cross-sections of particles of powder CE5 appears to be porous, while the matrix material observed by SEM microscopy of several cross-sections of particles of powders E1-E3 and C1-CE4 is dense and does not exhibit porosity.

[0133] [Example 4(E4) of the present invention] To produce the powder of Example 4 (E4), 20 g of the intermediate powder obtained in Example 2 was mixed with 20 g of graphite on a roller bench for 3 hours, and then the resulting mixture was passed through a mill to deagglomerate. Under these conditions, good mixing was obtained, but the graphite particles were not embedded in the pitch.

[0134] The resulting mixture is subjected to further heat treatment, namely, the product is 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 is carried out under an argon atmosphere.

[0135] The calcined product is then manually ground in a mortar and pestle and sieved through a 325-mesh sieve to form the final composite powder. The main physicochemical properties of the resulting powder E4 are reported in Table 2.

[0136] [Comparative Example 6 (CE6) not based on the present invention] To produce the powder of Comparative Example 6 (CE6), 20 g of the intermediate powder obtained in Comparative Example 2 was mixed with 20 g of graphite on a roller bench for 3 hours, and then the resulting mixture was passed through a mill to de-agglomerate. Under these conditions, good mixing was obtained, but the graphite particles were not embedded in the pitch.

[0137] The resulting mixture is subjected to further heat treatment, namely, the product is 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 is carried out under an argon atmosphere.

[0138] The calcined product is then manually ground in a mortar and pestle and sieved through a 325-mesh sieve to form the final composite powder. The main physicochemical properties of the resulting powder CE6 are reported in Table 2.

[0139] The specific surface area (BET value) of all powders is between 3.2 and 4.8 m². 2 It consists of / g

[0140] [Table 2]

[0141] Electrochemical evaluation of powders Powders E1-E3 and CE1-CE5 are tested in a coin cell according to the procedure specified above. The battery is stopped at the end of the first cycle, and the first lithiation capacity and first delithiation capacity are calculated.

[0142] Powders E1-E3 and CE1-CE5 are blended in a 1:1 mass ratio and further diluted with graphite.

[0143] Next, the diluted powders obtained from the E1-E3 powders and CE1-CE5 powders, as well as powders E4 and CE6, are tested in a coin cell according to the procedure specified above.

[0144] The results are reported in Table 3. The Coulomb efficiency and average Coulomb efficiency values ​​for the first cycle reported here are for diluted powders of E1-E3 and CE1-CE5, as well as pure powders of E4 and CE6, in order to compare cells containing anode materials of similar capacity.

[0145] [Table 3]

[0146] Comparing the results, it is clear that cells containing powders E1 to E4 according to the present invention as the negative electrode material have a higher Coulomb efficiency in cycle 1 and a higher average Coulomb efficiency in cycles 5 to 50 compared with cells containing powders CE1 to CE6 that do not conform to the present invention.

Claims

1. A powder suitable for use in the negative electrode of a battery, wherein the powder comprises particles, the particles comprising a matrix material and silicon-based subparticles embedded in the matrix material, the matrix material comprising a carbonaceous material, and the powder further comprising sulfur, wherein the weight content of sulfur in the powder is at least 0.1% of the weight content of the carbonaceous material and at most 1% of the weight content of the carbonaceous material.

2. The carbonaceous material contains graphite domains, and the graphite domains have a 2θ angle of 26° to 27°. Ｃｕ At maximum intensity I Ｃ The powder according to claim 1, having an average size of less than 10 nm when determined by the Scherrer equation applied to the X-ray diffraction peak of the powder assigned to C(002) having

3. When determined by nitrogen adsorption / desorption measurement, the result is 0.005 cm. ３ The powder according to claim 1 or 2, having a porous total specific volume less than / g.

4. The powder according to claim 1 or 2, wherein the carbonaceous material is soft carbon.

5. The powder according to claim 1 or 2, wherein at least 80% by weight of the sulfur contained in the powder is present in the matrix material.

6. The silicon-based subparticles are, ＮＳ Having a particle size distribution with a number reference of 50, the d ＮＳ The powder according to claim 1 or 2, wherein 50 is 40 nm or more and 150 nm or less.

7. The powder according to claim 1 or 2, wherein the silicon-based subparticles have a silicon weight content of at least 80% by weight.

8. The powder according to claim 1 or 2, wherein the powder has a silicon content A and an oxygen content C, both expressed as weight percent (wt%), and C ≤ 0.3 × A.

9. Maximum 10m ２ The powder according to claim 1 or 2, having a BET surface area of ​​1 / g.

10. The powder according to claim 1 or 2, further comprising graphite particles.

11. A method for preparing the powder according to claim 1 or 2, comprising the following steps: Step A provides a powder containing a carbon precursor, a powder containing silicon-based particles, and a powder containing sulfur. Step B involves mixing the powder containing the carbon precursor with the powder containing sulfur, and further heating the mixture while mixing to a temperature higher than the softening point of the powder containing the carbon precursor. Step C involves adding the powder containing silicon-based particles to the mixture obtained in step B and mixing it, The mixture is cooled to room temperature, followed by step D, in which the mixture obtained in step C is pulverized. A method comprising step E, in which the powder obtained in step D is heat-treated in an oxygen-free atmosphere at a temperature equal to at least 1000°C.

12. The method according to claim 11, wherein the weight content of sulfur in the mixture of step B is equal to at least 0.06% by weight and at most 0.65% by weight.

13. The method according to claim 11, wherein the carbon precursor is converted to soft carbon during the heat treatment of step E.

14. The method according to claim 11, wherein the carbon precursor is petroleum pitch.

15. A battery comprising the powder described in claim 1 or 2.

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