Silicon-based electrode material

Abstract

Silicon-based electrode material, comprising silicon nanoparticles and a mixed matrix of silsesquioxanes and silicon dioxide in which the silicon nanoparticles are embedded, wherein the mixed matrix comprises silicon with different oxidation states, and with an arrangement of Si-O-Si bonds capable of inducing: -an FTIR spectrum comprising, in the range from 950 to 1250 cm-1 a main peak characteristic of silicon dioxide, a pair of secondary peaks at wavenumbers higher than the main peak, and no peaks related to the Si-O-H bond at wavenumbers lower than the main peak, and - an NMR spectrum having a peak characteristic of silicon dioxide outside the range from -70 to -110 ppm, said NMR spectrum comprising, in the range from -70 to -110 ppm, a pair of peaks at chemical shifts lower than the peak characteristic of silicon dioxide, and having intensities greater than the peak characteristic of silicon dioxide.

Description

[0001] Silicon-based electrode material

[0002] The present invention generally relates to materials for lithium-ion batteries (LIB).

[0003] Lithium-ion batteries have garnered enormous scientific interest in recent decades due to their wide range of applications, such as electric transport and portable electronics. Furthermore, lithium-ion batteries are essential for storing energy produced from renewable sources such as wind and solar power. Therefore, as the demand for energy storage systems capable of delivering high energy and power density is constantly growing, the development of LIBs with higher energy density and longer cycle life is crucial for the new challenges of the energy transition.

[0004] Currently available LIBs use synthetic or natural graphite as the anodic active material, which hosts lithium ions through an intercalation mechanism. Graphite has high electrical conductivity, an excellent lithium-ion diffusion coefficient, and good stability during cycling, making it an ideal material for energy storage applications. On the other hand, the intrinsic nature of the material leads to a low specific gravimetric capacity (372 mAh g '), thus reducing the storable energy in a cell stack. Furthermore, natural graphite is a critical raw material and the production step of both artificial and natural graphite are responsible for significant CO2 emissions per year.

[0005] For these reasons, cleaner materials with higher energy density that exploit alternative storage mechanisms are the subject of intense scientific research. For example, silicon (both amorphous and crystalline) has been studied for many years as a potential candidate to replace common anodic materials in LIBs. Silicon reacts with lithium ions through an alloying process to form LiisSi4 as a discharge product, thus providing an extremely high gravimetric capacity (3700 mAh g-1). Furthermore, silicon is considered a promising material due to its abundance, low cost, and suitable operating voltage. However, during lithiation processes, silicon undergoes significant volume expansion (300%). The volumetric discrepancy between the lithiated and unlithiated counterpart can cause cracking and pulverization of the anode with consequent loss of active material and poor electrochemical performance. Moreover, silicon exhibits low electrical conductivity (~104S cm ') and a low Li+diffusion coefficient (~1013cm2s '), which hinder proper electron exchange during charge-discharge cycles. These drawbacks are slowing the adoption of pure silicon anodes in commercial energy storage devices. In fact, considering the LIBs currently available, the main component of the anodic material is still graphite with a low percentage of silicon, in the order of 10%-20% of the active material, in order to increase the battery capacity.

[0006] Numerous studies have been published to understand how to overcome the above-mentioned barriers and to advance a new battery technology that includes fully silicon-based anodes. Nanostructuring of the anodic material, with size reduction of the silicon particles, has proven to be an effective approach to cope with the large volumetric expansion of the electrode during cycling. In fact, particles with a diameter smaller than 150 nm are below the critical size for crack propagation, thus preventing electrode pulverization and increasing the electrochemical performance of the cell. For this reason, silicon nanoparticles, nanotubes, and nano wires have been synthesized to mitigate the volumetric effect and facilitate ion diffusion inside the electrode. To prevent the agglomeration of the aforementioned structures, researchers have attempted to immobilize the nanometric silicon within a host matrix (based on carbon, silicon oxides, etc.). The addition of a second material has the dual function of increasing the conductivity of the electrode — and consequently its rate capability — and further reducing the stress induced by lithium insertion. The combination of these approaches has proven to be an encouraging way to improve the performance of predominantly silicon-based anodes.

[0007] One object of the present invention is to make available a predominantly silicon-based electrode material that exhibits relatively low volumetric expansion following lithium insertion. Another object of the invention is to make available a predominantly silicon-based electrode material that exhibits relatively high stability during charge and discharge cycles. A further object of the invention is to make available an electrode material that exhibits a relatively high specific capacity.

[0008] To this end, the invention relates to a silicon-based electrode material, comprising silicon nanoparticles and a mixed matrix of silsesquioxanes and silicon dioxide in which the silicon nanoparticles are embedded, wherein the mixed matrix comprises silicon with different oxidation states, and with an arrangement of Si-O-Si bonds capable of inducing:

[0009] -an FTIR spectrum comprising, in the range from 950 to 1250 a main peak characteristic of silicon dioxide, a pair of secondary peaks at wavenumbers higher than the main peak, and no peaks related to the Si-O-H bond at wavenumbers lower than the main peak, and

[0010] -an NMR spectrum having a peak characteristic of silicon dioxide outside the range from -70 to -110 ppm, said NMR spectrum comprising, in the range from -70 to -110 ppm, a pair of peaks at chemical shifts lower than the peak characteristic of silicon dioxide, and having intensities greater than the peak characteristic of silicon dioxide.

[0011] In the present invention, silicon (amorphous or crystalline) incorporated in an inorganic matrix of silsesquioxanes arranged as open cages, rings, networks, ladder configurations or ladder-like configurations is proposed as a predominantly silicon-based anode material for LIBs. Silsesquioxanes have been studied as precursors to produce solid polymer electrolytes due to their high ionic conductivity and their thermal and structural stability. Moreover, they have been used as silicon and silicon oxide precursors, as fillers in nanocomposites, and in surface chemistry. Silsesquioxanes have never been used as a host matrix for silicon nanoparticles in lithium-ion battery anodes. In fact, one aspect of the invention concerns an anode comprising silicon nanoparticles incorporated in a matrix composed of silicon dioxide and mixed silsesquioxanes. Without being bound to any theory, it is hypothesised that in this architecture the silsesquioxanes act as a flexible binder between the more rigid silicon dioxide nanoislands. The matrix adapts to volume changes during lithiation, thus relieving internal stresses and preventing anode degradation. The proposed material can be used as an electrochemically active material for energy storage applications in pure form (about 100%) or in composition with other active materials, such as graphite, or in mixture with a binder and a conductive agent.

[0012] According to one embodiment, the silicon nanoparticles have diameters ranging from 0.1 to 150 nm, preferably from 1 to 50 nm, more preferably from 1 to 15 nm.

[0013] According to one embodiment, said mixed matrix around the silicon nanoparticles has a thickness ranging from 0.1 to 10 nm, preferably from 0.5 to 2 nm. According to one embodiment, said mixed matrix comprises different phases of silsesquioxane represented by the formula [RSiOsAJn, and silicon dioxide.

[0014] In particular, said silsesquioxane phases are selected from the group consisting of cages, open cages, rings, network configurations, polymeric configurations, ladder configurations, and ladder-like configurations.

[0015] The silicon nanoparticles may be of amorphous or crystalline silicon, preferably amorphous.

[0016] Preferably, said silicon-based material comprises Si and C with respective atomic percentages pSi and pC respectively ranging from 40 to 60%, and from 0 to 10%, preferably with a C content between 0 and 2%, and further comprises O with an atomic percentage pO equal to pO = 100% - pSi - pC.

[0017] The invention also relates to an anode for a lithium battery comprising a substrate and at least one layer comprising a silicon-based material according to the invention.

[0018] Said at least one layer may comprise the silicon-based material according to the invention mixed with a binder and a conductive additive.

[0019] Alternatively, said at least one layer may comprise the silicon-based material according to the invention coupled with another electrochemically active material.

[0020] In particular, the substrate is of a material selected from the group consisting of copper, molybdenum, stainless steel, carbon paper, carbon fabric, carbon felt.

[0021] Further features and advantages of the invention will be described in the following detailed description, which refers to the accompanying drawings, provided solely by way of example and not limitation, in which:

[0022] - Figures la, lb and 1c are respectively an HRTEM image and the related distribution maps of O2 and Si of a sample according to the invention;

[0023] - Figure 2 is a graph showing the XRD spectrum of the sample according to the invention;

[0024] - Figures 3a and 3b are respectively a graph showing the Raman spectrum of the sample according to the invention and a detail of the area between 60 and 600 cm1of said spectrum;

[0025] - Figures 4a and 4b are respectively a graph showing the FTIR spectrum of the sample according to the invention and a detail of the area between 950 and 1250 cm1of said spectrum;

[0026] - Figure 5 is a graph showing the XPS spectrum of the sample according to the invention;

[0027] - Figures 6a and 6b are graphs respectively showing the NMR spectrum with the magic angle spinning (MAS) of29Si of the sample according to the invention and the SiO? spectrum as reference;

[0028] - Figure 7 is a schematic representation of the internal structure of the sample according to the invention;

[0029] - Figures 8a and 8b are SEM images of an electrode according to the invention, respectively in a cross-sectional view and in a top view;

[0030] - Figure 9 is a graph showing a cyclic voltammetry trace of the electrode according to the invention;

[0031] - Figures 10a and 10b are graphs respectively showing a galvanostatic cycling test and a rate capability test of the electrode according to the invention;

[0032] - Figure 11 is a graph showing the capacity retention of a cell according to the invention after the 20th cycle;

[0033] -Figures 12a-c are graphs showing FTIR spectra of three respective samples according to the invention;

[0034] - Figure 13 is a graph showing the galvanostatic cycling of the three samples of figures 12a-c.

[0035] The present description relates to an active material for anodes and to anodes and lithium batteries containing the same. More particularly, it describes an anode for lithium-ion batteries based on an active phase comprising silicon nanoparticles, hereinafter also referred to simply as SNs, (diameter <150 nm, doped or undoped, amorphous or crystalline) enclosed in a mixed matrix of silsesquioxanes and silica (SiCF), hereinafter also referred to simply as MSSM.

[0036] Such material can be prepared by a plasma-assisted nanoparticle jet deposition technique, also known as NANOJED [1]. After deposition on a substrate (e.g., copper, copper meshes, carbon fabric, carbon paper), a compact fdm up to 200 pm of MSSM-SNs is obtained. The coated substrate is immersed in ethanol before being thermally treated at 700°C under vacuum.

[0037] Figure la shows the HRTEM (high-resolution transmission electron microscopy) analysis of an MSSM-SNs sample. The image reveals the presence of spherical globules of the active material with a homogeneous distribution and a diameter ranging from 1 to 15 nm. The coexistence of SNs and the surrounding matrix of silicon dioxide and silsesquioxanes is evident in Figures lb and 1c, which respectively show the distributions of O2 and Si in the same investigation area of the sample. Indeed, a high concentration of silicon with the formation of well-distributed agglomerates within the oxide phases is observed, justifying the sample morphology. MSSM acts as an ion-conducting scaffold that provides good structural stability during the charge and discharge cycles in LIBs. The most remarkable feature of MSSM is that it is also electrically conductive, allowing for the fabrication of thick electrodes (over 60 pm) without the addition of conductive phases such as carbon or similar materials.

[0038] XRD (X-ray diffraction) analysis of the sample confirmed the low degree of crystallinity of the constituent phase, and the results are shown in Figure 2, compared with the reference pattern of Si [2] [3]. In fact, the presence of two broad bands at 27° and 51° confirms the amorphous structure of the SNs [4] in the material and that of the surrounding matrix. The silicon incorporated in the MSSM can be amorphous or nanocrystalline, with a crystalline grain size ranging from 0.5 to 10 nm.

[0039] The amorphous nature of both the SNs and the MSSM is confirmed by the Raman spectrum shown in Figures 3a-b. Here, four bands are present at 150 cm 290 cm 380 cm1and 480 which respectively indicate the transverse acoustic (TA), longitudinal acoustic (LA), longitudinal optical (LO), and transverse optical (TO) modes. The TA / TO ratio of the material is between 0.5 and 0.75, confirming the amorphous state of the material, while the shift towards the blue of the TO peak indicates a high level of residual stress induced by lattice distortion within the MSSM [5], Moreover, the bands present at 620 cm1and 950 cm1qualitatively suggest a low level of hydrogenated silicon and the presence of amorphous silsesquioxane structures [6, 7].

[0040] The MSSM is characterised by a specific arrangement of Si-0 bonds allowing for the formation of a Si-O-Si polymeric structure around the SNs, comprising various phases of silsesquioxane, namely cages, open cages, rings, network configurations, polymeric configurations, ladder configurations or ladder-like configurations [8], as highlighted by the FTIR (Fourier Transform Infrared) spectroscopy analysis in Figure 4, wherein Figure 4a shows the complete spectrum and Figure 4b the area of interest. In fact, in the region between 950 and 1250 the characteristic band associated with the asymmetric stretching of the Si-O-Si bonds [9] of the MSSM structure is evident. More precisely, the region near 1100 cm1is a distinctive feature of the proposed material. Indeed, the broad band located in this spectrum region can be fitted with three different Gaussian curves, relating to the asymmetric stretching of Si-O-Si bonds with various angles between 130° and 180° [8].

[0041] At 1048 ± 20 ladder or ladder-like Si-O-Si structures can be found. The band that falls at 1139 ± 20 cm1is due to cage or cage-like structures with a Si-O-Si bond angle greater than 150°. At 1192 ± 20 cm ', out-of-plane Si-0 stretches are found [7a], The random structure of the SS includes various arrangements, including linear, branched, ladder-like, cyclic, strained cyclic, and cage-like structures; hence, the Si-O-Si stretching vibration appears as a broad band at 1150-1000 cm1[8, 9], More generally, the increase in the Si-O- Si bond angle has been correlated with a shift towards the blue of the corresponding FTIR Si-O-Si peak

[0010] , The peak at 801 cm1is associated with the Si-O-Si stretching of the SiO? phase, while the peaks around 950 cm1can be respectively attributed to the Si-OH and Si- O bonds.

[0042] The FTIR spectroscopy measurements discussed in the present description were conducted on samples deposited on a copper substrate using the Bruker Vertex 70 instrument. The instrument employs the attenuated total reflectance (ATR) sampling technique in a range between 200 and 2400 The measurement was conducted at room temperature with background subtraction.

[0043] The oxidation state of silicon within the nanostructured material was evaluated using XPS (X-ray photoelectron spectroscopy) and is shown in Figure 5. The acquired spectrum shows several oxidation states:

[0044] - Si(0) corresponding to elemental silicon,

[0045] - Si(I), Si(II) related to the presence of silsesquioxanes,

[0046] - Si(IV) related to the SiCh phase.

[0047] The analysis confirms the presence of metallic silicon in the SNs and in the oxide phases, i.e. ranging from 15% to 45%, in some cases between 20% and 40%, and in other cases from 25% to 35%. The atomic percentage of the active material composition is as follows: elemental silicon from 25% to 45%, and SS plus SiCh from 75% to 55%

[0011] ,

[0048] For a definitive differentiation between SS and SiO? or other silsesquioxane phases with the generic formula [RSiChA],,, the29Si NMR (nuclear magnetic resonance) spectrum is shown in Figure 6a, while the29Si NMR of silica is shown for comparison in Figure 6b. The NMR analysis of MSSM-SNs shows the presence of five peaks in region D (from -2 to -50 ppm), in the range of amorphous silicon (from -40 to -80 ppm) and in region Q (from -70 to -110 ppm)

[0012] attributed to the different structures of polyhedral oligomeric silsesquioxanes (POSS). The large broadening of the peaks can be attributed to the presence of amorphous phases within the sample, as anticipated by the XRD and Raman spectra

[0013] . The peak at - 30.7 ppm is attributed to the D2 structure denoted as cycle[R2SiO]4 which corresponds to a six-membered ring arrangement, also evidenced by the band at 490 cm1in the Raman spectrum. The peak at -58.9 ppm could be attributed to amorphous silicon aggregates

[0014] . The main peak in the Q region of the NMR spectrum was fitted with two peaks at -84.1 and -92.5 ppm respectively. The first could be associated with the Qi structure in the form SiOSi(OR)(OH)2 while the second with the cyclic species Q2 (SiO)2Si(OR)OH. The peak associated with Q4 (SiCh) is shifted from its typical chemical shift (-109 ppm) indicating a Si-O-Si bond angle greater than 150°, as suggested by the FTIR analysis

[0015] . Figure 6b shows the NMR of silica in which only the peaks at -100 and -110 ppm are present, attributable respectively to Q2 and Q3 regions

[0016] ,

[0049] The solid-state NMR measurements discussed in the present description were conducted using the Bruker AV500 HD NMR spectrometer, operating at Larmor frequencies for29Si andrH of 99.34 and 500.13 MHz respectively, and using a 3.2 mm double -resonance MAS probe. For cross polarization (CP), a ramped radiofrequency field was applied to therH channel. The CP contact time was 3 ms with 5120 transients and a recycle delay of 5 s was used. The 90° pulse length was 1.8 ms forrH and 3.5 ms for13C. A Q8M8 standard at 2.0 ppm was used as the external reference for29Si.

[0050] The peculiar configuration of the MSSM-SN sample can be schematically represented in Figure 7. Indeed, from the proposed analyses, the structure appears to consist of a broad distribution of metallic silicon domains 10 encapsulated within an MSSM 20 (in Figure 7, 30 also denotes residual silicon oxide with the formula SiCL, while d denotes the scale, e.g., 5 nm). This architecture hinders excessive swelling of the SNs during lithiation and adapts to internal stresses, leading to an improvement in the extractable capacity from the cells

[0017] . Furthermore, the resulting structure could enable coalescence of the matrix that strengthens the connection between the SNs and acts as a controlled inorganic interface for the formation of the solid electrolyte interphase (SEI) during the first lithiation cycle

[0018] .

[0051] The following describes a possible example of a method for preparing an electrode with the above-described material:

[0052] 1. direct deposition of the silicon-based active material onto a copper current collector (or Mo, SS, carbon paper, carbon fabric, carbon felt) by NanoJeD (nanoparticle jet deposition. This technique essentially consists of two phases: (i) production of silicon nanoparticles in a low-pressure non-thermal plasma (nucleation chamber); (ii) acceleration of the synthesized nanoparticles in a supersonic jet and growth by impact of a thin film on a substrate (impact chamber));

[0053] 2. the electrode is exposed to an oxidizing atmosphere (air in the proposed example) for a time between 1 s and 24 h, preferably 1 hour; 3. the electrode is immersed in an alcohol with variable chain length for a time between 1 minute and 4 hours, preferably 1 hour;

[0054] 4. the wet electrode is thermally treated under vacuum with a heating temperature ramp >150 °C / s up to 700°C and held at 700°C for a time between 15 and 30 min;

[0055] 5. the electrode is finally cooled to room temperature with a ramp >150 °C / s.

[0056] An alternative process for producing the anodes is as follows:

[0057] 1. preparing a slurry with Si nanoparticles, preferably with a diameter less than 100 nm, more preferably less than 10 nm, and even more preferably amorphous, with an organic solvent;

[0058] 2. depositing the slurry on a current collector by blade coating, spraying, or other methods to achieve a loading of up to 4-5 mg / cm2;

[0059] 3. thermal treatment of the "green" electrode under vacuum with a heating temperature ramp >150 °C / s up to 700°C and maintaining at 700°C for a time between 15 and 30 minutes;

[0060] 4. the electrode is finally cooled to room temperature with a ramp >150 °C / s.

[0061] The electrochemical behaviour of the electrode made with the proposed MSSM-SNs material is studied through cyclic voltammetry (CV) and galvanostatic charge / discharge tests to assess its suitability as a negative electrode in LIBs. Metallic lithium is used as the counter electrode in the half-cell configuration and a IM solution of lithium hexafluorophosphate (LiPFe) in ethylene carbonate and dimethyl carbonate (1 : 1 v / v, LP30) and vinylene carbonate (VC, 3vol%) is used as the electrolyte. The structure and morphology of the obtained electrode are shown in Figures 8a-b, wherein Figure 8a shows the silicon- based active material deposited on a copper foil with a uniform thickness of about 30 pm. Figure 8b shows the top view of the electrode. The image reveals the nanostructure of the electrode, wherein Si-based globules have aggregated due to the presence of MSSM. The electrode layer features open cavities, with an estimated porosity of about 80%, calculated from SEM analysis. However, the electrical connection is maintained and ensured by the presence of the MSSM.

[0062] The electrochemical reactions of the active material are studied by cyclic voltammetry (CV), shown in Figure 9. The test is carried out in a voltage range between 0.01 and 1.5 V. The voltammogram shows the presence of three different peaks in the reduction curve, which are correlated to the alloying process

[0019] . The cathodic peak at around 0.45 V could be attributed to the formation of lithium silicates

[0020] , while the subsequent peaks at around 0.2 V and 0.01 V are commonly attributed to the insertion of lithium into the structure of amorphous silicon. More specifically, the first is associated with the transition of silicon to the LiSi or LivSis phase, while the second refers to the further reduction of LiSi / LivSis to LiisSi4 as the final discharge product

[0021] , These last two reactions provide the major contribution in terms of specific capacity. The anodic curve in Figure 9 shows two distinct peaks between 0.35 and 0.5 V which are attributed to the delithiation of the silicon alloys from the EiisSi4 phase to the EivSis phase, further reduced to amorphous Si.

[0063] The galvanostatic cycling and rate capability tests of the MSSM-SNs sample are shown in Figures 10a and 10b. During the galvanostatic cycling test, carried out at a current density of 0.4 A g the cell based on MSSM-SNs demonstrated stable behaviour after repeated charge and discharge cycles (Figure 10a). The initial capacity of the cell is about 1400 mA h g stabilising within 10 cycles at around 1000 mA h g a capacity maintained for the following 180 cycles. The capacity fluctuations observed are due to temperature variations. Figure 10b shows the rate capability test carried out by increasing the current from 0.4 A g1to 7.5 A g passing through 1.3 A g1and 4 A g and finally returning to 0.4 A g '. At 0.4 A g the cell showed an initial capacity of 1350 mA h g which decreased after 10 cycles to 1170 mA h g '. At a higher current rate (4 A g '), the cell maintained a specific capacity of 200 mA h g reaching nearly 20 mA h g1when the current was further increased to 7.5 A g1. Once the current was returned to the original value, the sample recovered the capacity achieved after the initial stabilisation process (1100 mA h g-1).

[0064] Furthermore, the Si-based electrode was tested in a full cell configuration using commercial NMC111 as the cathodic material. Figure 11 shows the capacity retention (CR) of MSSM- SNs / NMCl l l after the initial activation cycles. The CR stabilises at a value of 99% after the initial stabilisation.

[0065] Example 1 To demonstrate the effectiveness of MSSM in mitigating the volumetric expansion of silicon during lithiation, the materials of the invention were compared with and without the ethanol pretreatment. For brevity, the samples are referred to as:

[0066] - Sample A according to the invention for the material (MSSM-SNs) which, after being deposited via nanoJeD, underwent ethanol treatment and rapid thermal treatment;

[0067] - Comparative Sample B for the material without ethanol treatment but which underwent rapid thermal treatment - this material lacks a fully developed silsesquioxane structure;

[0068] - Comparative Sample C for the material just deposited via nanoJeD, thus without ethanol treatment and without rapid thermal treatment.

[0069] The Si-O-Si bonds of the SS present in the MSSM include cage, cage-like, ladder, ladderlike, and occasionally linear chain structures. The balance between cage-like (polyhedral) and network-like (cross-linked ladder and linear chain) bonds influences the electrochemical performance of the proposed material. In Sample A (material of the invention, Fig. 1 la), the Si-O-Si bond angles expand to 150° or more, a typical value of cage-like structures. In this case, the Si-O-Si peak shifts to a higher frequency, reaching about 1190 cm1in the FTIR spectrum. Sample B also contains network-like structures, wherein the bond angle decreases to less than 144°, shifting the Si-0 peak to a lower energy level, around 1030 cm Samples B and C have an additional peak attributed to the presence of the Si-OH bond in the structure. In the FTIR spectra shown in Figure 12, the Si-O-Si bond angle of Sample B (Fig. 11b) measures 144°, with the asymmetric Si-0 stretching peak located at -160 typical of the SiO? structure.

[0070] Figure 12 shows an example of the FTIR spectrum of an SN coated with SiO? (Sample C), as evidenced by the presence of the main SiO? peak positioned at -1060 cm1typical of SiO? and a small secondary shoulder. The presence of a secondary peak positioned at 1108 cm1(still within the SiO? range) and the absence of a third peak at higher wavenumbers demonstrate the absence of SS phases in the structure of Sample C. Si-OH in the region below 1000 cm1is still present in Sample C. In conclusion, Sample A does not exhibit the -OH termination, shows a shift towards the blue of the silsesquioxane signal, suggesting the presence of distorted structures such as cage-like and ladder-like with bond angles greater than 150°, and ladder-like structures justified by the shift towards the of the main Si-O-Si peak with bond angles less than 144°.

[0071] Sample B exhibits a less distorted Si-O-Si structure, contains OH terminations, SiO?, and more linear SS structures. The electrochemical performance of Samples A, B, and C was compared and is shown in Figure 13. Sample A shows the best stability performance with a high specific capacity exceeding 1000 mA h g1for over 150 cycles. Sample B shows poor capacity below 400 mA h g while Sample C exhibits the worst electrochemical behaviour, highlighting the beneficial effect of the formation of cage and ladder silsesquioxane structures in a fully developed MSSM.

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Claims

CLAIMS1. A silicon-based electrode material comprising silicon nanoparticles and a mixed matrix of silsesquioxanes and silicon dioxide in which the silicon nanoparticles are embedded, wherein the mixed matrix comprises silicon with different oxidation states, and with an arrangement of Si-O-Si bonds capable of inducing: an FTIR spectrum comprising, in the range of 950 to 1250 cm-1, a main peak characteristic of silicon dioxide, a pair of secondary peaks at higher wavelength numbers than the main peak, and no peaks related to the Si-O-H bond at lower wavelength numbers than the main peak, and an NMR spectrum having a peak characteristic of silicon dioxide outside the range from -70 to -110 ppm, said NMR spectrum comprising, in the range from -70 to -110 ppm, a pair of peaks at chemical shifts lower than the silicon dioxide characteristic peak, and having intensities greater than the silicon dioxide characteristic peak.

2. The silicon-based electrode material according to claim 1, wherein the silicon nanoparticles have diameters between 0.1 and 150 nm, preferably between 1 and 50 nm, more preferably between 1 and 15 nm.

3. The silicon-based electrode material according to claim 2, wherein said mixed matrix around the silicon nanoparticles has a thickness between 0.1 and 10 nm, preferably between 0.5 and 2 nm.

4. The silicon-based electrode material according to any one of the preceding claims, wherein said mixed matrix comprises different silsesquioxane phases and silicon dioxide.

5. The silicon-based electrode material according to claim 4, wherein said silsesquioxane phases are selected from the group consisting of cages, open cages, rings, network configurations, polymeric configurations, ladder configurations and ladder-like configurations.

6. The silicon-based electrode material according to any one of the preceding claims,wherein the silicon nanoparticles are of amorphous or crystal-line silicon, preferably amorphous.

7. The silicon-based electrode material according to any one of the preceding claims, wherein said material comprises Si and C with respective atomic percentages pSi and pC respectively between 40 and 60%, and between 0 and 10%, preferably with a C content between 0 and 2%, and further comprises O with an atomic percentage pO equal to pO = 100% - pSi - pC.

8. An anode for a lithium battery comprising a substrate and at least one layer comprising a mate-rial according to any one of the preceding claims.

9. The anode according to claim 8, wherein said at least one layer comprises the material according to any one of claims 1 to 7 mixed with a binder and a conductive additive.

10. The anode according to claim 8, wherein said at least one layer comprises the material according to any one of claims 1 to 7 coupled with another electrochemically active material.

11. The anode according to any one of claims 8 to 10, wherein said substrate is of a material selected from the group consisting of copper, molybdenum, stainless steel, carbon paper, carbon fabric, carbon felt.

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