Composite powder for use in the negative electrode of a battery and a battery containing such composite powder

Abstract

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

Description

[Technical Field]

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

[0002] Lithium-ion (Li-ion) batteries are currently the most powerful batteries available and have already become the standard for portable electronic devices. In addition, these batteries are rapidly gaining popularity in other industries such as automotive and energy storage. The advantages of such batteries lie in their high energy density combined with excellent power performance.

[0003] Li-ion batteries typically consist of several so-called Li-ion cells, each comprising 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 have been developed using electrochemical active materials such as lithium cobalt oxide or lithium nickel manganese cobalt oxide for the cathode 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 anode. 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 70% of its initial discharge capacity. Therefore, most research on silicon-based electrochemically active powders focuses on improving this cycle life.

[0006] A drawback of using silicon-based 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 lead to gradual mechanical degradation of the silicon 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 between the electrolyte and lithium, leading to a loss of lithium's availability for electrochemical reactions and thus poor cycle performance, which is a loss of capacity per charge-discharge cycle. A thick SEI can further increase the battery's electrical resistance, thereby limiting its ability to discharge and charge at high currents.

[0008] In principle, SEI formation is a self-terminating process that stops as soon as a "passivation layer" 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 recharge (delithiation), thereby releasing a new silicon surface and initiating the formation of new SEI.

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

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

[0012] UK Patent No. 2563455 discloses a granular material composed of a plurality of composite particles. The composite particles include a plurality of silicon nanoparticles dispersed in a conductive carbon matrix. The contribution of the conductive carbon matrix in the Raman spectrum of the granular material is identified by a large G band and a prominent D band. In UK Patent No. 2563455, neither the presence of the D' band nor the technical effects related to the intensity ratio I D / I D’ are described at all.

[0013] International Publication No. 2022074031 discloses a powder of carbonaceous matrix material particles in which silicon-based sub-particles are dispersed. In International Publication No. 2022074031, Raman data is not disclosed.

[0014] European Patent No. 3113261 discloses a negative electrode material for a non-aqueous electrolyte secondary battery. The negative electrode material includes a conductive powder composed of silicon-based active material particles coated with a conductive carbon film. The conductive carbon film has a peak intensity ratio l D / l G [l DThis is the peak intensity of the D band, and l G The peak intensity of the G band is shown, and the D and G bands are determined from the Raman spectrum of the conductive carbon film. In European Patent No. 3113261, the presence of the D' band is also shown, as is the ratio of the intensities of the D band and the D' band. D / I D’ Nothing is said about the related technical effects.

[0015] International Publication No. 2010 / 065739 has up to four bands, or approximately 1360 cm. -1 (D band), approximately 1580cm -1 (G band), approximately 1620cm -1 (D' band), and approximately 2660cm -1 The present invention discloses a manufactured article comprising a carbon-containing matrix having a Raman spectrum with a band in the (DP band). International Publication No. 2010 / 065739 discloses the ratio of the intensity of the D band to the D' band. D / I D’ There is no mention of the related technical effects, nor of the silicon-based particles embedded in the carbon-containing matrix.

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

[0017] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 0198863 [Patent Document 2] British Patent No. 2563455 [Patent Document 3] International Publication No. 2022 / 074031 [Patent Document 4] European Patent No. 3113261 [Patent Document 5] International Publication No. 2010 / 065739 [Overview of the project] [Problems that the invention aims to solve]

[0018] The object of the present invention is to provide a composite powder containing composite particles, wherein the composite particles include a carbon matrix material in which silicon-based particles are embedded, and the composite powder is advantageous in that, once used as the negative electrode of a battery, it can achieve high capacity with a long cycle life. [Means for solving the problem]

[0019] This objective is achieved by providing a composite powder according to the present invention, which, when used in the negative electrode of a battery, enables the achievement of high capacity combined with a long cycle life, as demonstrated in Examples 1-3 compared to Comparative Examples 1-3. [Brief explanation of the drawing]

[0020] [Figure 1] This is a diagram of the Raman spectrum of a graphite material. [Figure 2] This is the Raman spectrum of composite powder E1 obtained using peak fitting. [Modes for carrying out the invention]

[0021] 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. Conversely, the present invention includes numerous substitutes, modifications and equivalents, as will become apparent from considering the embodiments for carrying out the present invention and the accompanying drawings.

[0022] In a first embodiment, the present invention relates to a composite powder for use in the negative electrode of a battery, comprising composite particles, wherein the composite particles comprise a carbon matrix material and silicon-based particles embedded in the carbon matrix material, and the composite powder has a Raman spectrum obtained by Raman scattering, wherein both the D band and the D' band correspond to the contribution of the carbon matrix material, and 1330 cm⁻¹ -1 ~1360cm -1 I D and 1600cm -1 ~1620cm -1 I D’ Each has its own maximum intensity, and ratio I D / I D’ However, this pertains to composite powders where the ratio is at least 0.9 and at most 4.0.

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

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

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

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

[0027] Silicon-based particles embedded in a carbon matrix material either form aggregates smaller than 1 μm in size or do not form any aggregates at all. Therefore, in the composite powder according to the present invention, the silicon-based particles are preferably in contact only with each other and / or only with the carbon matrix material.

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

[0029] In the Raman spectrum of graphite materials such as the composite powder carbon matrix material according to the present invention, the most prominent feature is typically around 1580 cm⁻¹. -1 The so-called G-band appears at approximately 1350 cm. -1 The D band appears at approximately 1610 cm. -1 The D' band appears, and approximately 2700 cm -1This is the G' band (also called the 2D band) that appears. Figure 1 shows a typical Raman spectrum of a graphite material that has four different bands.

[0030] The presence of the G band is characteristic of in-plane vibration modes associated with sp2 hybridized carbon. The D and D' bands are defect-induced Raman properties and cannot be seen in highly crystalline carbon materials with few defects. Intensity ratio I for the D and G bands D / I G This is often used to identify the amount of defects in graphite materials.

[0031] However, within the framework of the present invention, the inventors have indicated, as shown elsewhere in this specification, a different intensity ratio, namely, the ratio of the D band to the D' band. D / I D’ Then, I noticed a surprisingly direct correlation between battery performance and other factors.

[0032] The inventors of the present invention, D / I D’ However, the concentration of defects and changes in edge, vacancy-like defects, boundary-like defects, or carbon hybridization (e.g., sp 2 from sp 3 We believe it is a good indicator of both types of defects related to changes in this area.

[0033] Ratio I D / I D’ A value greater than 4.0 is undesirable because it indicates that the concentration of defects in the carbon matrix material is too high, which could negatively affect, for example, the electronic conductivity of the composite particles. Furthermore, this is undesirable because the defects are considered detrimental to the battery's cycle life. 3 It could also indicate that it's a "more damaging" type, such as something related to hybridization.

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

[0035] In other words, ratio I D / I D’ The technical effects related to this are greatest between 0.9 and 4.0.

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

[0037] In another embodiment according to the first aspect of the present invention, the carbon matrix material is soft carbon. Soft carbon corresponds to an arrangement 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.

[0038] 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 is reduced during anode lithiation compared to particles containing a matrix material that is mostly graphite or graphene. Reduced volume expansion leads to a longer battery cycle life.

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

[0040] Composite powders with a silicon content of less than 10% by weight, preferably less than 20% by weight, have excessively limited specific capacity and therefore cannot achieve the high energy density of the battery. Composite powders with a silicon content exceeding 60% by weight, preferably exceeding 50% by weight, expand excessively in relation to this high silicon content, resulting in a battery with a shortened cycle life.

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

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

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

[0044] Composite powders with excessively high oxygen content undergo additional irreversible lithium consumption during the initial lithiation of the powder, resulting in the formation of lithium silicate (Li2SiO3, Li4SiO4), thereby increasing the initial irreversible capacity loss of batteries containing such composite powders.

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

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

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

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

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

[0050] The d50 value is not considered to be affected by the process used to produce the composite powder, meaning that the d50 value of the silicon-based powder used as a precursor in the process is the same as the d50 value of the silicon-based particles contained in the composite powder.

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

[0052] As already mentioned, a negative effect associated with silicon is that thick SEIs, or solid electrolyte interfaces, can form on the anode, particularly on silicon-based particles. Because silicon-based particles are subject to large volume changes during the lithiation / delithiation process within the battery, already formed SEIs can be destroyed again, leading to continuous lithium consumption and a significant reduction in the battery's cycle life. Protecting the surface of silicon-based particles, at least partially, with a carbon matrix material is an effective solution to the continuous formation of SEIs and the resulting decrease in cycle life.

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

[0054] Preferably, the silicon-based particles do not contain elements other than Si and O in order to avoid the specific volume of the silicon-based particles being too low. The silicon-based particles mainly contribute to the specific volume of the composite 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 which case it is preferable that it be at least 80% by weight, preferably at least 90% by weight.

[0055] In another embodiment according to the first aspect of the present invention, the composite powder also comprises graphite particles and / or graphene particles, wherein neither the graphite particles nor the graphene particles are embedded in the carbon matrix material. “Neither the graphite particles nor the graphene particles are embedded in the carbon matrix material” means that less than 10% of the surface of the graphite particles and / or graphene particles is coated with the carbon matrix material, preferably less than 5% of the surface is coated with the carbon matrix material, and more preferably their surfaces are not coated at all with the carbon matrix material. This can be visually confirmed by analyzing one or more SEM images of cross-sections of the composite powder. The fact that the graphite particles and / or graphene particles are not embedded in the matrix material has the advantage of requiring less carbon matrix material, which has high irreversible capacity and low specific capacity, because only the silicon-based particles need to be coated with the carbon matrix material.

[0056] However, there may be some contacts located on the outer surface between the composite particles and the graphite and / or graphene particles. This is even more preferable in order to ensure good electronic conductivity of the composite powder and therefore high rate capacity of the battery containing the composite powder.

[0057] Furthermore, the graphite particles act as spacers between the composite particles, preventing them from agglomerating 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. This weakens the integrity of the matrix material and ultimately leads to lower performance in batteries containing such agglomerated powder.

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

[0059] These graphite materials may affect the Raman spectrum of the composite powder, so the ratio of the contribution of the carbon matrix material, especially the contribution to the D and D' bands, is important. D / I D’ To obtain the desired result, these contributions must be removed. The procedure is described in detail in the "Analysis Method" section.

[0060] In yet another embodiment according to the first aspect of the present invention, the composite powder is at most 10 m 2 / g, preferably no more than 8m 2 It has a BET surface area of ​​ / g.

[0061] It is preferable that the composite powder has a low BET specific surface area and reduces the surface area of ​​electrochemically active particles that come into contact with the electrolyte, thereby limiting the formation of lithium-consuming SEIs and thus limiting the reduction in the cycle life of batteries containing such composite powders.

[0062] In another embodiment according to the first aspect of the present invention, the composite particles have a volume-based particle size distribution having D10, D50 and D90, where 1 μm ≤ D10 ≤ 10 μm, 5 μm ≤ D50 ≤ 25 μm and 10 μm ≤ D90 ≤ 40 μm.

[0063] To clarify, for example, if D50 is 15 μm, then in this specification, 50% by volume of the composite particles have a size smaller than 15 μm, and 50% by volume of the composite particles have a size larger than 15 μm.

[0064] Particles in matrix materials with a volume-based particle size distribution of D50 less than 5 μm may have an excessively high specific surface area, which can result in an increased surface area for reaction with the electrolyte and for SEI formation, and this is undesirable for the reasons explained above. Particles in matrix materials with a volume-based particle size distribution of D50 greater than 25 μm are more susceptible to breakage during lithium uptake due to their size, which can result in a shorter cycle life for batteries containing such particles.

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

[0066] The negative electrode typically includes a binder or a mixture of binders. Specific examples of binders include polysaccharides, lithium polyacrylate (Li-PAA), sodium polyacrylate (Na-PAA), potassium polyacrylate (K-PAA), polyacrylic acid (H-PAA), sodium carboxymethylcellulose (Na-CMC), and styrene-butadiene rubber (SBR). Binders are added to improve the cohesive force of the various components of the negative electrode, the mechanical strength on the current collector, or, further, the flexibility. The binder accounts for 1% to 15% by weight, particularly 2% to 10% by weight, of the total weight of the negative electrode layer (excluding the current collector). Examples of negative electrode preparations are described elsewhere in this specification.

[0067] Finally, the present invention also relates to a battery, preferably a lithium-ion battery, comprising a negative electrode according to the present invention and thus a composite powder according to the present invention prepared as defined or previously disclosed.

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

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

[0070] Analysis method used Measurement of silicon content The silicon content of the composite powder is measured using X-ray fluorescence (XRF) with an energy-dispersive spectrometer. This method has a stochastic experimental error of ±0.3 wt% Si.

[0071] Measurement of oxygen content The oxygen content of the composite powder is measured using a LECO TC600 oxygen-nitrogen analyzer in the following manner: The powder sample for analysis is placed in a closed tin capsule, which is then placed in a nickel basket. This 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 composite powder is measured using a Leco CS230 carbon-sulfur analyzer in the following manner: The sample is melted in a ceramic crucible in a high-frequency furnace 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 existing CO to CO2, all generated CO2 is finally detected by an infrared detector. The signal is then converted to the carbon content.

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

[0074] Determination of electrochemical properties The electrochemical properties of the composite powders in the examples and comparative examples are determined by the following method.

[0075] 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 composite powder / 1 wt of carbon black (C65) / 2 wts of carbon fiber (VGCF) and 8 wts of carboxymethyl cellulose (CMC). These components were mixed in a Pulverisette 7 planetary ball mill at 250 rpm for 30 minutes.

[0076] Copper foil cleaned with ethanol is used as the current collector. A 200 μm thick layer of the mixed components is coated onto the copper foil. Then, the coated copper foil is dried in a vacuum at 70°C for 45 minutes. 1.27 cm from the coated and dried copper foil. 2 A disc was punched out and used as an electrode in a coin cell that uses lithium metal as the counter electrode. The electrolyte was 1M LiPF6 dissolved in EC / DEC 1 / 1 + 2%VC + 10%FEC solvent.

[0077] All coin cells are cycled using a high-precision battery tester (Maccor 4000 series) according to the following procedure. During the cycle, "CC" represents "constant current" and "CV" represents "constant voltage".

[0078] ● 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 ● Cycle 2 and beyond: ○ 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

[0079] 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.

[0080] In subsequent cycles, even if the CE typically rises sufficiently to over 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).

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

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

[0083] To do this, cross-sections of a composite powder, each containing multiple cross-sections of composite particles, and each containing multiple cross-sections of silicon-based particles, are prepared according to the procedure detailed below.

[0084] 500 mg of the composite powder to be analyzed is embedded in 7 g of resin (Buehler EpoxiCure 2), which consists 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 for 12 seconds using a Cressington 208 carbon coater to obtain a sample, also called a "cross section," which will be analyzed by SEM.

[0085] Next, the prepared cross-section was examined using a Bruker Xflash5030-127 EDS detector (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.

[0086] 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.

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

[0088] To non-restrictively describe the measurement of the number-based particle size distribution of silicon-based particles, the procedure using SEM is shown below. 1. Obtain multiple SEM images of the cross-section of a composite powder containing silicon-based particles dispersed in it. 2. Adjust the image contrast and brightness settings to easily visualize cross-sections of composite particles and silicon-based particles. Due to their different chemical compositions, the difference in brightness allows for easy distinction between the two types of particles. 3. Using suitable image analysis software, select at least 1000 individual cross-sections of silicon-based particles from one or more acquired SEM images that do not overlap with other cross-sections of silicon-based particles. These individual cross-sections of silicon-based particles can be selected from one or more cross-sections of composite particles and composite powders containing silicon-based particles. 4. For each of at least 1000 individual cross-sections of the silicon-based particle, measure the size of the individual cross-section of the silicon-based particle using suitable image analysis software.

[0089] Next, the d10, d50, and d90 values ​​of the number-based particle size distribution of silicon-based particles obtained using the method described above 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.

[0090] Measurement of volume-based particle size distribution The volume-based particle size distribution of composite particles will be measured using a Malvern Mastersizer 2000 laser diffraction particle size analyzer. The following measurement conditions will be selected: Compression range, active beam length 2.4 mm, measurement range: 300 RF, 0.01~900 μm. Prepare and measure the sample according to the manufacturer's instructions.

[0091] Raman spectroscopy Using a 532nm laser excitation, we will perform Raman spectroscopy analysis of the composite powder using a Renishaw inVia Qontor Raman spectrometer.

[0092] To process the acquired spectrum, the following steps are performed. 1. Subtract the background by removing both cosmic ray and baseline contributions. 2. The obtained spectrum is fitted to three curves—D-band, G-band, and D'-band—using appropriate software, as shown in Figure 2. If graphite particles are present, first obtain the spectrum of pure graphite and subtract the contribution of the composite powder to the spectrum. If graphite particles are absent, all D, G, and D' bands will inevitably be contributions from the carbon matrix. 3. Measure the ID / ID' ratio.

[0093] Experimental preparation of the examples Comparative Example 1 (CE1) not based on the present invention To prepare the powder of Comparative 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 temperature to a uniform level (i.e., in the reaction zone) exceeding 2000K, thereby initially obtaining the silicon-based powder. In this first process step, the precursor was completely vaporized. In the second process step, 20 Nm was used to lower the gas temperature to below 1600K. 3 A stream of argon at 1 / hour is used as a quenching gas immediately downstream of the reaction zone to nucleate the silicon into metallic, submicron-sized silicon powder. Finally, a passivation process 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.

[0094] The specific surface area (BET) of the obtained silicon powder was measured to be 82 m². 2 The concentration is per gram. The oxygen content of the obtained silicon powder was measured to be 7.9% by weight. The number-based particle size distribution of the silicon powder was measured to be d10=52nm, d50=111nm, and d90=171nm.

[0095] Next, a dry blend is prepared from 100 g of the obtained silicon powder and 840 g of polyvinyl chloride (PVC) with a melting point of 160°C. The blend is heated to a temperature of 190°C under a nitrogen stream, and after a waiting time of 60 minutes, it is mixed for 30 minutes under high shear by a Cowles dissolver type mixer operating at 1000 rpm.

[0096] The mixture of silicon powder in PVC thus obtained is cooled to room temperature, solidified, then pulverized and sieved through a 400-mesh sieve to produce Intermediate Powder 1.

[0097] Next, 20 g of the obtained Intermediate Powder 1 is placed in a quartz crucible in a tubular furnace, heated to 900°C at a heating rate of 3°C / min, held at that temperature for 2 hours, and then cooled. All of these are carried out under an argon atmosphere. In the obtained product, silicon-based particles are dispersed and embedded in the matrix of soft carbon generated by the thermal decomposition of PVC.

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

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

[0100] When the total Si content of this powder is measured by XRF, it is 39.3 wt%, and the experimental error is ±0.3 wt%. This corresponds to the value calculated based on the weight loss of about 84 wt% of PVC during heating and the slight weight loss of other components during heating. The calculated ratio of the carbon content generated by the carbonization of PVC forming the matrix material to the silicon content in the powder is about 1.46. When the oxygen content of this powder is measured, it is 3.4 wt%. When the specific surface area (BET) of the obtained powder is measured, it is 3.3 m 2 / g.

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

[0102] Next, the powder of Comparative Example 1 is analyzed by Raman spectroscopy according to the procedure described above. 1344 cm⁻¹ -1 The intensity of the D peak located at 1610 cm -1 A ratio of 0.54 to the intensity of the D' peak located at [location] is obtained. This value is reported in Table 2.

[0103] Example 1 (E1) of the present invention The composite powder of Example 1 (E1) is prepared using the same method as the composite powder of Comparative Example 1 (CE1), except that the intermediate powder 1 is heated to 1000°C instead of 900°C.

[0104] The total Si content of this composite powder was measured by XRF to be 39.3% by weight. The oxygen content of this powder was measured to be 3.5% by weight. The specific surface area (BET) of the obtained powder was measured to be 3.2 m². 2 It is / g.

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

[0106] The Raman spectrum obtained for composite powder E1 is shown in Figure 2. 1344 cm⁻¹ -1 The intensity of the D peak located at 1610 cm -1 A ratio of 1.23 is obtained for the intensity of the D' peak located at [location].

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

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

[0109] Next, 20 g of the obtained intermediate powder 2 is placed in a quartz crucible inside a tubular furnace and heated to 900°C at a heating rate of 3°C / min. After holding at that temperature for 2 hours, it is cooled. All of these steps are carried out under an argon atmosphere. In the resulting product, silicon-based particles are dispersed and embedded in the soft carbon matrix produced by the thermal decomposition of PVC.

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

[0111] The total Si content in this powder was measured to be 39.2% by weight. This corresponds to a value calculated based on the weight loss of PVC during heating (approximately 82% by weight) and the slight weight loss of other components during heating. The calculated ratio of carbon content obtained from the carbonization of PVC in the powder to silicon content is approximately 1.47. The oxygen content of this powder was measured to be 3.4% by weight. The specific surface area (BET) of the obtained powder was measured to be 3.4 m². 2 It is / g.

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

[0113] Example 2(E2) of the present invention The composite powder of Example 2 (E2) is prepared using the same method as the composite powder of Comparative Example 2 (CE2), except that the intermediate powder 2 is heated to 1000°C instead of 900°C.

[0114] The total Si content of this composite powder was measured by XRF to be 39.2% by weight. The oxygen content of this powder was measured to be 3.6% by weight. The specific surface area (BET) of the obtained powder was measured to be 3.5 m².2 It is / g.

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

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

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

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

[0119] When the total Si content of this composite powder is measured by XRF, it is 17.0 wt%. When the oxygen content of this powder is measured, it is 1.5 wt%. When the specific surface area (BET) of the obtained powder is measured, it is 3.3 m 2 It is / g.

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

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

[0122] The resulting mixture of silicon powder in phenolic resin is cooled to room temperature, allowed to solidify, then pulverized and sieved through a 400-mesh sieve to produce intermediate powder 3.

[0123] Next, 20 g of the obtained intermediate powder 3 is placed in a quartz crucible inside a tubular furnace and heated to 1000°C at a heating rate of 3°C / min. After being held at that temperature for 2 hours, it is cooled. All of these steps are performed under an argon atmosphere. In the composite powder of Comparative Example 3, unlike the composite powder obtained earlier, silicon-based particles are dispersed and embedded in a matrix of hard carbon produced by the thermal decomposition of phenolic resin.

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

[0125] The total Si content in this powder, as measured by XRF, is 39.2% by weight. This corresponds to a value calculated based on the weight loss of approximately 25% by weight of the phenolic resin during heating and the slight weight loss of other components during heating. The calculated ratio of carbon content obtained from the carbonization of the phenolic resin in the powder to silicon content is approximately 1.47. The oxygen content of this powder is measured to be 3.4% by weight. The specific surface area (BET) of the obtained powder is measured to be 4.2 m². 2 It is / g.

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

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

[0128] Comparing the results of the composite powder from E1 to E3 according to the present invention with those of the composite powder from CE1 to CE3, for the aforementioned possible reasons, the ratio I is 0.9 to 4.0, particularly 1.0 to 3.0, and even more particularly 1.0 to 2.6. D / I D’ It was found that the best results were obtained in cells containing a composite powder having [specific characteristic]. [Table 2]

Claims

1. A composite powder for use in the negative electrode of a battery, comprising composite particles, wherein the composite particles comprise a carbon matrix material and silicon-based particles embedded in the carbon matrix material, and the composite powder has a Raman spectrum in which both the D band and the D' band correspond to the contribution of the carbon matrix material, at 1330 cm⁻¹. －１ ~1360cm －１ I Ｄ and 1600cm －１ ~1620cm －１ I Ｄ’ Each has its own maximum strength, and ratio I Ｄ / I Ｄ’ However, the composite powder is at least 0.9 and at most 4.

0.

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

0.

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

6.

4. The composite powder according to claim 1, wherein the carbon matrix material is soft carbon.

5. The composite powder according to claim 1, having a silicon content S expressed in weight percent (weight%), wherein 10% by weight ≤ S ≤ 60% by weight.

6. The composite powder according to claim 1, having a carbon content C expressed in weight percent (weight%), wherein 30% by weight ≤ C ≤ 90% by weight.

7. The composite powder according to claim 1, having a silicon content S and an oxygen content N, both expressed as weight percent (weight%), and N ≤ 0.20S.

8. The composite powder according to claim 1, wherein the silicon-based particles are characterized by a number-based particle size distribution having d50, and d50 is 20 nm or more and 150 nm or less.

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

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

11. The composite powder according to claim 1, further comprising graphite particles and / or graphene particles, wherein less than 10% of the surface of the graphite particles and / or graphene particles is coated with the carbon matrix material.

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

13. The composite powder according to claim 1, wherein the composite particles have a volume-based particle size distribution having D10, D50, and D90, and the particle sizes are 1 μm ≤ D10 ≤ 10 μm, 5 μm ≤ D50 ≤ 25 μm, and 10 μm ≤ D90 ≤ 40 μm.

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

15. A battery comprising the negative electrode described in claim 14.

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