KR102016929B1 - Black phosphorus/carbon nanotube composite material having high-capacity and ultradurable properties, method for producing the composite material, and electrode comprising the composite material - Google Patents

Abstract

The present invention comprises the steps of milling red phosphorus to synthesize black phosphorus; Mixing the synthesized black phosphorus and carbon nanotubes while being exposed to air; It provides a method for producing a black-carbon nanotube composite comprising the step of milling the air-exposed black phosphorus and carbon nanotube mixture, and also provides an electrode using the prepared composite.

Description

Black phosphorus / carbon nanotube composite material having high-capacity and ultradurable properties, method for producing the composite material, and electrode comprising the composite material }

The present invention relates to a black lean / carbon nanotube composite material having a high capacity and long life characteristics, a manufacturing method thereof and an electrode comprising the same.

Black phosphorus (BP) is a promising layered material, and has recently been considered for a variety of high-tech applications, mainly due to its high carrier mobility, anisotropic electronic properties and adequate band gap. In the corrugated layered structure, each phosphorus atom is connected with two other atoms on the same plane and with one or more atoms in adjacent planes, creating a ₆ -atomic P ₆ ring similar to a layered material such as other graphene. In addition, BP has been investigated as the anode material of lithium ion and sodium ion cells (LIB and NIB, respectively) due to the high theoretical specific capacity of 2596 mAh / g (Li ₃ P and Na ₃ P during discharge in LIB and NIB, respectively). Assuming its formation). In addition, BP has a suitable electrical conductivity (0.2-3.3 × 10 ² S / cm), an appropriate density (2.69 g / cm 3), a thermodynamically stable structure, an appropriate charge / discharge potential range, and Li ⁺ and Na ⁺ insertion / deinsertion. It has a high speed during the process.

However, large volume changes in BP during cycling (about 300% and 500% in LIB and NIB, respectively) cause severe grinding of BP, resulting in rapid capacity reduction after only a few cycles. As such, black lean, which is a negative electrode material of a lithium ion or sodium ion battery, causes electrode detachment due to a large volume change during charging and discharging, thereby degrading the life characteristics of the electrode.

An object of the present invention is to provide a black lean / carbon nanotube composite material having a high capacity and long life characteristics, a manufacturing method thereof and an electrode comprising the same.

The present invention, in order to achieve the above object, the step of milling red phosphorus to synthesize black phosphorus; Mixing the synthesized black phosphorus and carbon nanotubes while being exposed to air; It provides a method for producing a black lean-carbon nanotube composite comprising the step of milling the air-exposed black lean and carbon nanotube mixture.

In the black lean synthesis step of the present invention, red phosphorus may be milled in an inert gas atmosphere.

Inert gas in the present invention is argon, milling can be carried out using a planetary ball mill.

The ball-to-powder (BPR) mass ratio is 40 ± 10: 1, the milling speed is 450 ± 100 rpm, and the milling time may be 10 to 80 hours in the blacklin synthesis step of the present invention.

In the present invention, the mixing ratio of black phosphorus and carbon nanotubes may be 5 to 9: 1 to 5 as a weight ratio.

In the present invention, the air exposure time may be 20 to 60 minutes.

Using a planetary ball mill in the milling step of the black phosphorus and carbon nanotube mixtures according to the invention, the ball-to-powder (BPR) mass ratio is 20 ± 10: 1, the milling speed is 300 ± 100 rpm and the milling time May be 10 to 80 hours.

Through milling in the present invention, amorphous red phosphorus can be converted to crystalline black phosphorus.

The content of the crystalline phase in the black lean synthesized in the present invention may be 60% or more.

Through air exposure in the present invention, it is possible to oxidize the surface of the black lean surface hydrophilicity of the black lean hydrophobic.

In the present invention, hydrophilic surface-modified black phosphorus may form strong P-O-C bonds with carbon nanotubes.

Through air exposure in the present invention, black phosphorus can include hydrophilic and defective surface layers and lattice defects and adsorbed oxygen atoms.

Through air exposure in the present invention, phosphorus pentoxide may be formed in black phosphorus.

In the present invention, phosphorus pentoxide can react with water to form phosphoric acid, thereby functionalizing the carbon nanotubes.

Through milling in the present invention, it is possible to weaken the sp ² -type carbon of the carbon nanotubes, form a lattice point, adsorption atoms, edges and gaps in the carbon nanotubes, and increase the active site of the carbon nanotubes.

In the present invention, the milled carbon nanotubes have a D band to G band (I _D / I _G ratio) of 1.3 or more, a G-band frequency of 1591 cm ^-1 or more, and a percentage of sp ² -type carbon of 80% or less. Can be.

In addition, the present invention provides an electrode using a black lean-carbon nanotube composite, a conductive agent and a binder prepared according to the above-described method as the active material.

In the present invention, the binder may be a two-component binder.

The binder in the present invention may include at least two or more of polyvinylidene fluoride, sodium carboxyl methyl cellulose, poly (acrylic acid).

In the present invention, the conductive agent may be carbon black.

In the present invention, the mixing ratio of the composite: conductive agent: binder may be 70 ± 10: 15 ± 10: 15 ± 10 as the weight ratio.

In the present invention, black phosphorus may bind to the binder through P-O-C chemical bonding and dehydration crosslinking.

In the present invention, crosslinks may be formed between the carbon nanotubes and the binder and between the binders.

In the present invention, the electrode can be used as an anode of a lithium ion battery or a sodium ion battery.

In the lithium ion battery according to the present invention, the discharge capacity of the electrode is 1600 mAh / g or more after 400 cycles at a current density of 0.2 C, and may maintain a capacity of 80% or more based on the first discharge capacity.

In the sodium ion battery according to the present invention, the discharge capacity of the electrode is 1500 mAh / g or more after 200 cycles at a current density of 0.2 C, and may maintain a capacity of 70% or more based on the first discharge capacity.

According to the present invention, a black phosphorus / CNT complex having a strong chemical bond with a binder may be synthesized and prepared as an electrode. This strong structure can suppress electrode breakage during charging and discharging, thereby improving life characteristics. In addition, excellent electrical contact with the conductive agent may improve high rate characteristics. In addition, in the present invention, the surface of the non-hydrophilic black phosphorus is oxidized in the air to perform surface modification, thereby improving the bond with CNT (P-O-C) and the cross-link with Na-CMC and PAA binder.

1 is a graphical comparison of existing research and various inventive strategies for various RP-carbon composites. As indicated by FIG. 1A, it is important in the present invention to perform a two-step ball milling process to obtain the final BP-CNT composite. When performing ball milling through the existing process of FIG. 1B, the presence of CNTs inhibits the conversion of amorphous RP to crystalline BP. As demonstrated below, the first step forms a hydrophobic BP, which is modified by controlled air exposure, resulting in modified and defective hydrophilic BP. The modified BP can stably bind to the CNT after long milling in the second step, and can also stably bind to the bicomponent binder during electrode manufacture through two distinct POC chemical bonds and dehydration crosslinking.
2A is an XRD pattern of CNTs, BP30, BP60, and four designated BPC complexes according to FIG. 1A and listed in Table 1. FIG. FIG. 2B is an XRD pattern of CNT, RP and two RPC composites obtained from one-step ball milling of the RP + CNT precursor of FIG. 1B after 30 and 50 hours milling. The results clearly show the final product different from that obtained using FIG. 1A (two-step milling). 2C shows the calculated content of milling time versus BP crystalline phase, based on the XRD pattern. Lorentzian fitting was used to calculate the data from the XRD in FIG. 2C. Inset is the ³¹ P MAS-ssNMR spectrum of BP60. Sharp peaks at 15 ppm confirm the formation of pure BP nanocrystals after 60 hours of milling. All spinning sidebands are marked with a *.
FIG. 3A compares the I _D / I _G ratio and phonon frequency of Raman G mode with sp ² -type carbon percentage (obtained from EELS measurements) in Pristine CNT and BPC1-BPC5 complexes. The results in FIG. 3A are averaged over 10-15 individual spectra taken from different sites of the sample. Increased error is associated with increased non-uniformity of the results. Lorentzian fittings were used to calculate data for Raman analysis. FIG. 3B is an EPR spectrum of BPC1 and BPC4 again showing high content of oxygen functional groups and imperfections in the walls and ends of the shortened CNTs. 3C shows the phosphorus L _2,3 and oxygen K (inset) edge spectra of BP60 (before controlled air exposure), BPC4 and BPC5 measured by EELS, clearly confirming the effect of surface oxidation during controlled air exposure. An additional P ₂ O ₅ signal appeared in the spectrum of BPC4, while negligible in BPC5. 3D is the FT-IR spectra of Pristine CNTs, BP60 (before and after air exposure), BPC4 and BPC5. 3E is anion spectra from ToF-SIMS of BP60 (before and after air exposure), BPC4 and BPC5 samples, demonstrating significant hydrophilic properties in BPC4 compared to BPC5. FIG. 3F is the detailed PO ⁻ and CPO ⁻ (inset) ToF-SIMS spectra of FIG. 3E. The large OH ^- peak in FIG. 3E and the very small CPO ^- in the inset of FIG. 3F for BPC5 perfectly confirm the FT-IR results associated with the occurrence of two distinct POC chemical bonds and dehydration crosslinking in BPC4. It also highlights the need and importance of controlled air exposure that makes BP hydrophilic. 3G is ¹³ C MAS-NMR spectra of BPC1 and BPC4. The content of -OH functional groups in BPC4 is less than that of BPC1, which also confirms the ability of hydrophilic BP to stably link to CNTs through an esterification reaction. 3H is a TG curve of pristine CNTs, BPC3, BPC4 and BPC5 in air or Ar atmosphere. Additional weight loss (indicated by two arrowheads) suggests high amounts of crosslinking and chemical bonding in BPC4.
The upper part of FIG. 4 schematically shows the BP-CNT active material with carbon black and binder applied on Cu foil for electrochemical testing. The lower part of FIG. 4 shows different electrode components: (i) between hydrophilic and defective BP and functionalized CNTs, (ii) between BP and two crosslinked binders, (iii) functionalized CNTs and dehydration reactions. It represents all possible forms of POC chemical bonds and dehydration crosslinks formed between the binders formed through. The binders may be linked to one another during the same dehydration process, as indicated by (iv), wherein the free carboxylic acid groups of the PAA form covalent ester bonds with the —OH groups of NaCMC.
5A is FT-IR spectra of PAA and NaCMC, mixed c-NaCMC-PAA binder, and BPC4-c-NaCMC-PAA. 5B is a ¹³ C MAS-NMR spectrum of BPC1-c-NaCMC-PAA and BPC4-c-NaCMC-PAA. 5C is a TG curve of BPC3-c-NaCMC-PAA and BPC4-c-NaCMC-PAA.
6A is the initial charge-discharge voltage profile of BPC1-BPC5. FIG. 6B shows the cycle stability of the BPC1-BPC4 samples at 0.2 C (1 C = 2596 mAh / g) and 0.01-2.0 V for LIB, stable chemistry at BPC4 due to lower polarization compared to other samples Demonstrate the binding clearly. 6C compares the rate performance of four BPC1-BPC4 samples for LIB at current densities of 0.2-4.5 C. FIG. 6D shows the markedly high rate cycle stability of BPC4 for LIB, with a final capacity of 903 mAh / g at 1 C for 100 cycles and then 4.5 C for 200 cycles. The first 10 cycles were performed at 0.2 C for proper activity. 6E shows the cycle stability of BPC4 for NIB at a current density of 0.2 C and 0.01-2.0 V. 6F shows the rate characteristics of BPC4 for NIB up to very high 4.5 C. FIG. 6G shows the superior fast cycle stability of BPC4 for NIB at a final capacity of 700 mAh / g at 1 C for 100 cycles and then at 2 C for 200 cycles. The first 10 cycles were tested again at 0.2 C for the activation process. All electrodes were made with c-NaCMC-PAA binder and capacity results based on the mass of BP.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The method for producing a black phosphorus-carbon nanotube composite according to the present invention is characterized by a two-stage milling process and controlled air exposure, thereby providing an electrode for a high capacity long life lithium ion battery or sodium ion battery.

Specifically, the method for producing a black phosphorus-carbon nanotube complex according to the present invention comprises the steps of synthesizing black phosphorus by milling red phosphorus; Mixing the synthesized black phosphorus and carbon nanotubes while being exposed to air; Milling the air-exposed black phosphorus and carbon nanotube mixtures.

In the black phosphorus synthesis step, red phosphorus may be milled in an inert gas atmosphere such as argon. The milling may be ball milling, preferably by using a planetary ball mill. The milling of the black phosphorus synthesis step is the first step milling or the first milling. Through first stage milling, amorphous red phosphorus can be converted to crystalline black phosphorus. Accordingly, the content of the crystalline phase in the synthesized black phosphorus may be 60% or more (100% or 95% or less), preferably 70% or more, more preferably 90% or more.

The ball-to-powder (BPR) mass ratio in the blacklin synthesis step may be 40 ± 10: 1, preferably 40 ± 5: 1. The milling speed may be 450 ± 100 rpm, preferably 450 ± 50 rpm. The milling time may be 10 to 80 hours, preferably 30 to 70 hours, more preferably 50 to 70 hours.

The mixing ratio of the black phosphorus and carbon nanotubes in the mixing step may be 5-9: 1-5, preferably 6-8: 2-4 as a weight ratio. The air exposure time in the mixing step can be 20 to 60 minutes, preferably 30 to 45 minutes.

Through air exposure, the surface of the black rinse can be oxidized to hydrophilically modify the black rinse, which was hydrophobic. Hydrophilic surface-modified black phosphorus can form strong P-O-C bonds with carbon nanotubes. In addition, through air exposure, black phosphorus can contain hydrophilic and defective surface layers and lattice defects and adsorbed oxygen atoms. In addition, through air exposure, phosphorus pentoxide may be formed in black phosphorus. Phosphorous pentoxide formed at this time may react with water to form phosphoric acid, thereby functionalizing the carbon nanotubes.

The milling step of the black phosphorus and carbon nanotube mixtures is the second stage milling or the second milling. The milling here may also be ball milling, preferably using a planetary ball mill. Here, the ball-to-powder (BPR) mass ratio may be 20 ± 10: 1, preferably 20 ± 5: 1. The milling speed may be 300 ± 100 rpm, preferably 300 ± 50 rpm. The milling time may be 10 to 80 hours, preferably 20 to 60 hours, more preferably 40 to 60 hours.

Through milling, it is possible to weaken the sp ² -type carbon of the carbon nanotubes, form a lattice point, adsorption atoms, edges and gaps in the carbon nanotubes, and increase the active sites of the carbon nanotubes. The D band to G band (I _D / I _G ratio) of the milled carbon nanotubes may be 1.3 or more (1.6 or less), preferably 1.4 or more. The G-band frequency may be at least 1591 cm ⁻¹ (up to 1630 cm ⁻¹ ), preferably at least 1600 cm ⁻¹ . The percentage of sp ² -type carbon may be 80% or less (50% or more), preferably 60% or less.

In addition, the present invention provides an electrode using a black lean-carbon nanotube composite, a conductive agent and a binder prepared according to the above-described method as the active material.

The binder may be a binary binder. For example, the binder may include at least two or more of polyvinylidene fluoride, sodium carboxyl methyl cellulose, and poly (acrylic acid). Preferably it may be a bicomponent binder composed of sodium carboxymethyl cellulose and poly (acrylic acid). Carbon black etc. can be used as a electrically conductive agent. The mixing ratio of the composite: conductor: binder may be 70 ± 10: 15 ± 10: 15 ± 10, preferably 70 ± 5: 15 ± 5: 15 ± 5 as weight ratio.

In the electrode according to the present invention, black phosphorus may bind to the binder through P-O-C chemical bonding and dehydration crosslinking, and crosslinking may be formed between the carbon nanotubes and the binder and between the binders.

The electrode according to the invention can be used as the anode of a lithium ion battery or a sodium ion battery.

In the lithium ion battery according to the present invention, the discharge capacity of the electrode may be 1600 mAh / g or more (1800 mAh / g or less) after 400 cycles at a current density of 0.2 C, and 80% or more (90%) based on the first discharge capacity. Up to%), preferably at least 85% capacity.

In the sodium ion battery according to the present invention, the discharge capacity of the electrode is 1500 mAh / g or more (1700 mAh / g or less) after 200 cycles at a current density of 0.2 C, and 70% or more (80% or less) based on the first discharge capacity. ), Preferably at least 75% capacity.

In general, there are three main methods for synthesizing black phosphorus (BP), namely the chemical vapor transport method (CVT developed by Nilges et al.), The high pressure-high temperature method (HPHT pioneered by Bridgman), and ball milling. Among them, high-energy milling is a simple and up-scaleable technique that does not require special machines or complicated manufacturing steps. In addition, BP synthesized by CVT and HPHT could hardly exhibit satisfactory electrochemical performance.

In particular, BP has much better electrical conductivity than amorphous red phosphorus (RP). And, due to its layered structure, BP can exhibit better electrochemical performance than RP.

In addition, carbon nanotubes (CNT) can provide excellent ability to accommodate volume expansion of BP. CNTs are well known to act as buffers to absorb stresses due to conductive networks and volumetric variations, mainly due to their unique one-dimensional (1D) structure with low electrical resistance and strong mechanical properties.

Importantly, ball milling has proven to be the best strategy among feasible synthesis of functionalized CNTs because of the high reactivity of the CNTs and the high energy delivered to them during milling. By comparison, chemical methods such as reflux in strong inorganic acids or organic solvents present a variety of problems, including the quality, controllability of the final product and the risk of contamination and toxic chemicals.

As recent studies of other anode materials (eg Si, Ge and Sn) have confirmed, electrochemical properties such as irreversible capacity fading and cyclability strongly depend on the stability and strength of the entire electrode. . A common method of fabricating anodes for LIB and NIB cells consists of mixing the active material with a carbon conductive additive (such as carbon black) and a polymeric binder, followed by casting the mixture onto a copper foil as a current collector.

Well known binders include polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (NaCMC), poly (acrylic acid) (PAA), and the like, which bind electrode components by hydrogen bonding and / or van der Waals forces. Let it be. However, it is difficult to prevent or sufficiently minimize electrode breakage during cycling, mainly due to the low interaction between the binder and the active material.

In order to avoid this obstacle and to improve the stability of the electrode to realize a long life battery, the present invention utilizes a strong cross-linked interaction between ball-milled BP powder, functionalized CNTs and bicomponent binders to produce anodes. We have developed a simple, feasible and inexpensive approach.

The main issue in the present invention is to change the hydrophobic nature of BP nanocrystals to hydrophilic to form strong chemical bonds with functionalized CNTs, which are the most well known layered layers such as graphene and transition metal dichalcogenide. Because it is a common problem of materials. In the present invention, various characteristics evaluation methods were used to study the parameters affecting the binding between BP and CNT components.

In addition, the bicomponent, functional polymeric and cross-linked NaCMC-PAA (c-NaCMC-PAA) binders provided a strong connection with the BP-CNT active material, which (1) formed a strong structure and a charge / discharge process It was a very important approach to effectively prevent the failure of the whole electrode, to (2) prevent the loss of electrical contact between the electrode components, and (3) to ensure strong adhesion of the active material on the copper current collector. . The hydroxyl group of NaCMC and the carboxylic acid group of PAA have been found to be very effective in forming strong bonds with hydrophilic BP and functionalized CNTs.

As a result, the cross-linked BP-CNT composite electrode of the present invention could provide significant cycle performance and speed characteristics as anodes for LIB and NIB. The discharge capacity was 1681 mAh / g corresponding to 87.5% capacity retention after 400 cycles at a current density of 0.2 C for LIB, and 1560 mAh / g (75.2% capacity retention) after 200 cycles at the same current density for NIB, Initial CEs were 92.0% and 87.7% for LIB and NIB, respectively. The composites of the invention also exhibited good fast cycle characteristics in LIB and NIB applications, ie 1513 and 903 mAh / g after 100 and 200 cycles at 1 C and 2 C for LIB, and 1 C after 100 cycles for NIB. And 1050 and 700 mAh / g at 2 C. This attractive low-cost approach presented in the present invention can shed additional light on the use of new BP-based materials in a wide range of innovative counterparts and for a variety of applications.

EXAMPLE

1. Experiment section

(1) material

Commercial RP (Alfa Aesar, -100 mesh, 98.9%), MWCNT (Carbon Nanomaterial Technology Co. Ltd., Korea), PVDF (Sigma-Aldrich, Mw = 534000), PAA (Sigma-Aldrich, Mv = 3000000), and NaCMC (Sigma-Aldrich, Mw = 700000) was used as received without further purification.

(2) synthesis of BP

As a first step, the RP was placed in a stainless steel bayer and sealed in a glovebox under high purity argon protection, followed by ball milling with a Fritsch P6 planetary ball mill. The ball-to-powder (BPR) mass ratio was maintained at 40: 1 and the milling speed was maintained at 450 rpm for up to 60 hours. The BP30 and BP60 (milled for 30 and 60 hours, respectively) samples were then selected for the second milling.

(3) Synthesis of BP-CNT Complex

Milled BP30 and BP60 were mixed with MWCNT in air at a 7: 3 weight ratio for 30-45 minutes. The air-exposed BP and CNT mixture was then transferred to Bayer and milled for 20 and 50 hours at a BPR of 20: 1 and a speed of 300 rpm to prepare BP-CNT complexes (BPC1 to BPC4). Details of the milling steps are shown in Table 1. 1A shows various steps in the synthesis of the BP-CNT complex.

Designated name speed
(rpm) Milling time
(h) BPR BP: CNT
ratio air
exposure BP30 450 30 40: 1 - × BP60 450 60 40: 1 - × BPC1 (BP30 + CNT) 300 20 20: 1 7: 3 ○ BPC2 (BP30 + CNT) 300 50 20: 1 7: 3 ○ BPC3 (BP60 + CNT) 300 20 20: 1 7: 3 ○ BPC4 (BP60 + CNT) 300 50 20: 1 7: 3 ○ BPC5 (BP60 + CNT)
(Control test) 300 50 20: 1 7: 3 ×

(4) Synthesis of Control Test Sample

As a control test, to identify the need for two milling steps to reach the final BP-CNT homogeneous mixture, RP and CNTs mixed in the same ratio (7: 3) were added at 40: 1, as shown in FIG. 1B. Milling in one step for up to 50 hours at BPR and a speed of 450 rpm. Small amounts of powder were collected at specific time intervals to monitor the milling process.

In addition, one additional sample without controlled air exposure was designed to compare structural and electrochemical properties (BPC5 in Table 1). For this purpose, BP60 was carefully synthesized under ultrahigh-purity Ar gas, then mixed with CNTs inside an Ar filled glovebox and ball-milled again for 50 hours, similarly to BPC4 shown in Table 1.

(5) evaluation of characteristics

High-resolution powder X-ray diffraction (XRD) patterns were collected on a Rigaku diffractometer (40 kV, 40 mA) in Bragg-Brentano θ-2θ geometry using copper Kα radiation (λ = 0.154059 nm). The 2θ step size was 0.01 ° and the residence time per step was 5 seconds. XPS spectra were recorded on a K-alpha spectrometer (Thermo Scientific Inc., UK) using an Al Kα μ-focused monochromator (hν = 1486.6 eV). Main C 1s peaks were corrected with carbon black (284.6 eV) for high-resolution scans. Spectral peaks were deconvoluted using Lorentzian linear and Shirley background separation. Raman spectra were acquired on a LabRam Aramis (Horiba Jobin Yvon) instrument with an Ar laser source of 532 nm in a macroscopic configuration. Solid ¹³ C and ³¹ P MAS-NMR spectra were recorded using a Bruker Avance II 500 spectrometer (125.7 MHz) with a 4-mm diameter solid probe head and a ZrO ₂ rotor rotating at 10 kHz. Spectra were normalized by the mass of each sample. CW EPR spectra were recorded on a Bruker EMX plus spectrometer in the X band using a liquid He temperature control system (ER4112HV). Spectra were collected with the following experimental parameters and normalized per mass of each sample: microwave frequency of 9.64 GHz, microwave power of 1 mW, modulation amplitude of 1 G, and modulation frequency of 100 kHz. Experiments were performed at 4 K to reduce noise. TG curves were acquired using a TGA / DSC 1 (Mettler Toledo) analyzer and samples were placed in an alumina pan at 50 mL / min air or Ar flow at a constant heating rate of 10 K / min. FT-IR spectroscopy was performed with a Bruker (Model Vertex 70) spectrometer in diffuse reflection mode using the Spectra Tech Collector II accessory. ToF-SIMS (ToF-SIMS 5 spectrometer, ION-TOF) analysis was performed using a Bi ₃ ^{+ 2} beam operating at 30 keV with a current of 0.34 pA. Positive and negative spectra were obtained in the range of m / z = 0-500 with a scan area of 500 μm × 500 μm. BET surface area was measured by Quantachrome® ASiQwin ™ (Autosorb-iQ 2ST / MP) system using nitrogen adsorption at 77 K. The morphology of the ball-milled samples was evaluated by field emission scanning electron microscopy (FESEM, JEOL-7800F) using energy-dispersive X-ray spectroscopy (EDS) to semi-quantitatively examine the microstructures. TEM analysis was performed with a spherical aberration corrected scanning transmission electron microscope (Cs-corrected-STEM; JEM-ARM 200F, JEOL) operating at an acceleration voltage of 200 kV in combination with EDS and EELS analysis. EELS measurements were performed with another FEI Titan ™ HRTEM system using an acceleration voltage of 80-300 kV. Sp ² bonds (C = C bond fraction) in all considered counterparts were obtained by EELS analysis in the STEM mode of the carbon K edge-near structure using the following equation.

[Equation 1]

Where I ^u and I ^g are the integrated peak intensities of the composite and graphite, respectively.

For quantitative evaluation of the BP crystal phase at milling, the V _f value was calculated from the XRD profile. To this end, the integrated areas of amorphous and crystalline peaks were carefully separated by peak-fitting software, and the V _f of BP nanocrystals was estimated approximately as follows.

[Equation 2]

Where A _c and A _a are the total integral areas of the crystalline BP and amorphous RP phases, respectively. The 2θ range considered is divided into three distinct regions (10-20 °, 21-44 °, and 44-75 °) to fully cover the three major amorphous regions of RP in the XRD and compare them with the corresponding BP peaks. It was 10-75 degrees. For example, the RP 013 and BP 020 peaks were considered in the first range (10-20 °) for the ball-milled samples for 5-60 hours. In the second range, RP 318 was compared to four BP peaks, namely (021), (111), (002), and (131). Each ball-milled sample was carefully analyzed and the exact location of the XRD peak was determined by Lorentzian and Gaussian curve fitting found to be in good agreement with each other. However, only the values obtained from Lorentzian curve fitting are considered. This is because the V _f value determined from the error of the Lorentzian function has lower uncertainty than the Gaussian function. Error bars are also shown in FIG. 2C. Appropriate comparisons with nearly identical results can be performed with TEM images to distinguish between the two amorphous and crystalline phases.

(6) electrochemical test

For electrochemical measurements, CR2032 coin-type half cells were assembled using Li or Na metal as counter electrode inside the argon-filled glovebox. The electrode mixture contained one of the active materials (BPC1 to BPC5), carbon black as the conductive agent, and a binder in a weight ratio of 70:15:15. Binary crosslinked binders were prepared in a 1: 1 ratio of PAA (3 wt.%) And NaCMC (1 wt.%). The mixture was then doctor-bladed on a copper foil to a thickness of 10 μm. In addition, control experiments were performed using bare PAA, NaCMC, and PVDF binders to compare the performance of the electrode materials of the LIB. The prepared electrode was vacuum dried at 150 ° C. for 2 hours. Slurry loading on the electrode was 1.45-1.65 mg. The electrolyte was 1 M in a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (EC: DMC: DEC = 2: 2: 1 volume ratio) containing fluoroethylene carbonate (FEC, 10 vol.%) For the LIB test. LiPF ₆ ; For NIB experiments it was 1 M NaClO _{4 in} a mixture of 10 vol.% FEC plus EC: DEC (1: 1 volume ratio). Galvanostatic discharge / charge tests, CV, and EIS were performed using Princeton Applied Research VMP2 potentiostat / galvanostat. Charge / discharge tests were performed with Li / Li ⁺ or Na / Na ⁺ in the range of 0.01-2.0 V. The CV test was performed at a scan rate of 0.1 mV / s in the range of 0-2 V. EIS was performed by applying a perturbation voltage of 5 mV between 1 Hz and 10 ⁵ Hz.

2. Results and discussion

(1) structural change during synthesis

As shown in FIG. 1, BP was synthesized using commercial RP by mechanical ball-milling at 450 rpm for 30 and 60 hours (designated BP30 and BP60, respectively). As demonstrated by the XRD pattern and TEM image, during ball milling, extensive mechanical deformation provided sufficient energy to convert from amorphous RP to BP nanocrystals. In the next step, as shown in Table 1, the ball-milled BP and MWCNTs were mixed at a weight ratio of 7: 3 and milled at 300 rpm for 20 and 50 hours (FIG. 2A). It is worth pointing out that this two-step synthesis strategy is needed to generate the final BP-CNT complex (FIG. 1A). Direct ball milling of a mixture of RP and CNTs resulted in RP-CNT composites as evidenced by the XRD pattern of FIG. 2B even for a long time of 50 hours (FIG. 1B). The peak of the RP-carbon (RPC) composite rapidly widened after milling as compared to the starting materials (RP and CNT). This is due to the disappearance of the mid-range rule structure of the RP and the conversion to a very irregular amorphous structure by the addition of CNTs. This interesting finding can easily be extended to other BP-based carbon composites because, in all previous studies, ball-milled RP and carbon materials in one step could only form RP-based composites. Carbon materials are believed to inhibit the progression of amorphous RP to crystalline BP transitions, because they are very likely to absorb the energy transferred from the milling tool during ball milling, thus creating a barrier to this transition in RP. It takes away energy to overcome. However, as demonstrated by XRD and TEM analysis, bare BP could be easily synthesized in less than 10 hours in the present invention. XRD data were used to determine the content of crystalline BP (V _f ) as a function of milling time up to 60 hours (FIG. 2C). After 5 hours of milling the content of crystalline BP was only 12 ± 8%, but this percentage increased to about 94 ± 5% after 60 hours. ³¹ P solid magic angle spinning nuclear magnetic resonance (ssMAS-NMR) spectroscopy was used to verify the XRD and TEM results. The inset of FIG. 2C shows a sharp narrow NMR peak for pure BP at 15 ppm, which is consistent with previous reports. Additional characterizations were also performed on the synthesized samples and structural changes were discussed.

As theoretical calculations as well as recent experimental studies have demonstrated, oxygen can spontaneously dissociate single- or several-layered phosphorene at ambient conditions. This exothermic surface oxidation occurs to a lesser extent even in bulk BP powders and increases exponentially during the first few hours of air exposure. This reactivity between oxygen and BP is due to the latter sp ³ binding properties and gives hole electron pairs to all BP atoms. The main reaction product was found to be phosphorus pentoxide (P ₄ O ₁₀ or simply P ₂ O ₅ ) and is mainly present in the top layer of BP. As previously reported, pristine BP is naturally hydrophobic and therefore rarely reacts with H ₂ O. However, partial surface oxidation makes the surface more and more hydrophilic by effectively improving the adsorption energy of H ₂ O. Assuming that mild surface oxidation of the bulk BP powder can make it hydrophilic, by intentionally applying controlled air exposure to the BP, the protective oxide layer was successfully created, which is different from other electrode components (i.e. CNT and two binders). It could help form chemical interactions. The main products of the air treatment are BP with hydrophilic and defective surface layers and various forms of imperfections such as di-vacancy point defects and adsorbed oxygen atoms. The optimal duration of air exposure is important here because the various phosphorus oxides react spontaneously with H ₂ O through exothermic reactions. In addition, small side reactions between P ₂ O ₅ and free water are possible, which can be present in the milling bayer to form phosphoric acid (H ₃ PO ₄ ) and easily act as an activator to surface the CNT walls. Could be functionalized with Thus, in the present invention, the BP and CNT components were mixed in air for 30-45 minutes (Table 1, BPC1-BPC4), which is a duration experimentally found to be sufficient to obtain a stable oxidized surface layer and hydrophilic BP. The resulting air-exposed BP60 bound strongly to the binder (1) during subsequent ball milling after a given duration, and (2) through two distinct mechanisms: POC chemical bond formation and dehydration reaction. For comparison, another experiment was also conducted, which made a strong bond between the components to clearly highlight the important effects of the air exposure step, designated BPC5 in Table 1. Here, by using various characterization techniques, the two aforementioned mechanisms between all electrode components were investigated in detail. Electrochemical measurements for LIB and NIB applications will be presented later.

(2) Demonstration of Stable Bonding During Synthesis

First, the change in CNTs with different milling times was evaluated. Many researchers have reported fracturing and shortening of CNTs during the milling process. CNTs are generally very curved with several kinks and junctions. High-energy ball milling damages the structural integrity by weakening sp ² -type carbon and forming various types of disorders such as lattice points, adsorption atoms, edges, and interstitial. These structural imperfections are favorable for in-situ interfacial reactions. Thus, proper milling time improves accessible active sites (such as various functional groups and sp ³ -type defective carbon in the walls and ends of shortened CNTs), and CNTs through inter-tube dehydration. Creates stable crosslinks between and between CNTs and other components. As the high-resolution TEM image demonstrates, the CNT structure is damaged, exhibiting open tip and sidewall defects, providing high reactivity and diffusion. The d-values remained almost the same, which confirms that graphitization was only slightly affected by milling, and the structural change was local. In addition, H ₃ PO ₄ could be formed from the reaction of water and P ₂ O ₅ , thereby partially activating the surface of the CNT wall and also improving oxygen functionality.

Functionalization of CNTs in five samples (BPC1-BPC5) using short and long milling times (20 and 50 hours, respectively) was demonstrated by Raman and electron energy loss spectroscopy (EELS) measurements. 3A shows the relative integral intensity of the D band to G band (I _D / I _G ratio), the phonon frequency of the G band (both extracted from Raman spectra), as well as the Pristine CNT and the five milled composites. The content of sp ² -hybridized carbon (derived from the EELS analysis of the carbon K edge-near structure) is compared to provide information on the structural change in the CNTs. High I _D / I _G ratio and incompletely integrated SP ² in pristine CNTs The network indicates the presence of structural imperfections in the CNT network. When the CNTs were milled for only 20 hours, the I _D / I _G ratio did not show a significant change in BPC1 and BPC3 (Table 1). On the other hand, 50 hours of ball milling increased this value from 1.31 ± 0.06 in BPC1, to 1.43 ± 0.12 in BPC2 and about 1.46 ± 0.12 and 1.45 ± 0.10 in BPC4 and BPC5, respectively. Thus, significant structural defects were present in the ball-milled CNTs. The G-band frequency also showed the same trend, showing a maximum blue shift of 17.03 ± 10 cm ⁻¹ in BPC4 compared to Pristine CNT (1590.51 ± 10 cm ⁻¹ ), while this shift was BPC1 And negligible in BPC3. This blue shift exhibited increased compressive strain in three BPC2, BPC4 and BPC5 samples due to the long milling time, confirming the presence of some form of incompleteness on the CNT structure. Defects were also demonstrated from the percentage reduction of sp ² -type carbon after milling and reached the lowest values for BPC4 and BPC5 (56 ± 3% and 56 ± 2%, respectively). Carboxyl and hydroxyl groups are the most common functional groups on CNTs, which are responsible for the effective crosslinking of CNTs with hydrophilic BPs and binders at the electrodes.

Electron paramagnetic resonance (EPR) analysis was also performed to further compare the oxygen functionality and imperfections of the sample. 3B shows normalized EPR spectra per mass of each BPC1 and BPC4. The EPR spectrum of carbon radicals is typically a single broad resonance. The spectrum of BPC4 had a nearly similar linewidth (200 G vs. 180 G), but with higher intensity than BPC1, suggesting the presence of more radical and dangling bonds that are non-uniformly distributed in the CNT structure. . This clearly demonstrates abundant oxygen groups or defects in the wall or end of the shortened CNTs in BPC4.

In addition, EELS analysis was used to pinpoint the effect of controlled air exposure on the surface oxidation of BP. 3C shows the results for BP60, BPC4 and BPC5 samples. Only one characteristic core-loss peak was observed at 131.7 eV at BP60 before air exposure due to the PL _2,3 edge, while BPC4 had one additional signal at 137.6 eV, corresponding to P ₂ O ₅ . , Which indicates the presence of surface oxygen on air-exposed BP nanocrystals. As expected, BPC5 also showed only one peak at 131.8 eV due to the PL _2,3 edge, because there was no air exposure to this sample. The final BPC5 complex then had negligible surface oxidized BP. This was again demonstrated from the presence of the oxygen K (OK) -shell excitation edge at about 541 eV in BPC4, while not in BP60 and BPC5 (inset of FIG. 3C).

X-ray photoelectron spectroscopy (XPS) has also been used to compare oxidation changes during air exposure. BP60 (before air exposure), and the BPC4 and BPC5 - resolution P 2p showed, all the two strongest peaks, i.e. 2p _3/2 of the 2p _1/2 and 129.8 eV at 130.6 eV, as shown in the spectrum. In P it is been found that with only one oxidation state (P ^5+, 134.6 eV) only, which dropped to confirm that the oxidation product mainly P ₂ O ₅ once again, P ₂ O ₅ is BP60 and BPC5 but negligible, It was remarkable in the BPC4 complex. A significant increase in P ₂ O ₅ content in the final milled product of BPC4 compared to BPC5 strongly suggests the hydrophilic nature of adsorbing —OH functional groups to functionalized CNTs and binders.

The chemical states of BP, CNT, and the two BPC4 and BPC5 complexes were evaluated by Fourier Transform Infrared (FT-IR) spectroscopy. As shown in FIG. 3D, Pristine CNTs exhibited relatively strong bands at about 3200-3700 cm ⁻¹ due to OH bonds at the hydroxyl and carboxyl groups, and C = at 1574 and 1640 cm ⁻¹ , respectively. C and -C = O stretching vibrations were shown. Very small PO peaks at about 920 cm ⁻¹ at BP60 (before air exposure) again demonstrated very low oxygen content in this sample, and also a small —OH peak could be seen at about 3420 cm ⁻¹ . In contrast, this sample showed a large -OH peak after air exposure, the PO peak at 920 cm ^-1 became stronger, and another peak at 1182 cm ^-1 corresponds to a P = O bond (mainly P ₂ O ₅ and partly due to H ₃ PO ₄ ). As a result, BPC4 had three distinct peaks in the 900-1300 cm ⁻¹ range, highlighting the role of controlled air exposure in changing the hydrophobic nature of BP. The new clear peak centered at about 1002 cm ⁻¹ was due to POC stretching. The -C = O stretching vibration of the carboxylic acid at 1640 cm ^-1 was reduced through the dehydration reaction to form -COO groups compared to the Pristine CNT, which was modified by BP and modified adsorption of -OH functional groups by hydrophilic BP and Strong suggestion is to form strong crosslinks between CNTs. More importantly, a significant reduction in the -OH peak at about 3420 cm ^-1 is the main and convincing evidence for the presence of stable crosslinks between the BP and CNT components. However, this peak can be seen completely in BPC5, which indicates a negligible or insufficient esterification reaction due to BP not trying to link to the functionalized CNTs.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to show the hydrophobic nature and hydrophilicity of the ball-milled BP after controlled air exposure (FIG. 3E). As the results clearly show, limited oxygen adsorption made the surface hydrophilic, which is in full agreement with previous experiments and calculations. Obvious that the presence of high ionic strength of the upper surface of the BP is partly oxidized to be readily adsorbed an -OH functionality from the other ^{components-after} air exposure ^{O -, OH -, PO -} , PO 2 - and PO ₃ Confirm. Observation of strong OH ⁻ peaks in BPC5 confirmed the inadequate esterification reaction during the second stage ball milling, which was not completely present in BPC4. 3f compares the two PO ⁻ and CPO ⁻ peaks in the samples mentioned. Insets provide further evidence for POC chemical bonds in BPC4, which peaks were not significant in BPC5, consistent with XPS and FT-IR results.

In addition, ¹³ C MAS-NMR analysis was performed to investigate changes in the -COOH group centered at about 190 ppm. The comparison of BPC1 and BPC4 clearly shows a decrease in peak area in the latter, which again demonstrates more effective adsorption of -OH groups by BP after longer milling times. In addition, the C = C peak centered at about 119.1 ppm in BPC1 was shifted to 122.5 ppm in BPC4, indicating a percentage reduction of sp ² -type carbon in the latter due to long and severe mechanical deformation during milling. As a result, the amount of sp ³ carbon was slightly increased at ˜60 ppm.

To further identify abundant crosslinks and chemical bonds in the BPC4 complex, thermal properties were compared with other samples. Thermogravimetric analysis (TGA) was also used to confirm the content of phosphorus in the complex. 3h shows TG curves of CNTs, BPC3, BPC4 and BPC5, all analyzed in air atmosphere. Only two BPC3 and BPC4 had different milling times of the second stage, and BPC5 was a control sample with negligible crosslinking and chemical bonding (Table 1). In addition, BPC5 was analyzed in high purity Ar gas. All three composites analyzed in the air flow showed a nearly similar trend, ie the weight increased from about 100 ° C. to 480-520 ° C. due to oxidation, resulting in a drastic weight loss due to sublimation of phosphorus above. The BPC5 complex with minor chemical bonds and crosslinks showed a final 69% weight loss, nearly equal to the primary CNT and BP content. However, more structural defects were generated along the walls and ends of the CNTs during milling, as well as successful POC binding and -COO crosslinking resulted in additional 3% and 8% weight loss in BPC4 compared to BPC3 and BPC5 respectively. Induced (FIG. 4I). Thus, as can be easily concluded, the two-step ball milling process plus the controlled air exposure of BP is a reliable choice for the feasible synthesis of BP-CNT composites with strong chemical bonds for energy-related applications.

(3) Contribution of Binary Binder

Next, as shown in FIG. 4, the presence of a strong crosslink is demonstrated when a two-component binder is present. As a polymeric binder for better adhesion to electrode components, a three-dimensional (3D) network of bicomponent c-NaCMC-PAA was designed and fabricated. In this approach, BPC4 complexes have been successfully embedded in flexible 3D binder matrices with well-established, interconnected, cross-linked networks with permanent covalent bonds. This structure was able to provide superior chemical and mechanical properties as well as amazing electron conduction networks compared to other binders, thus effectively accommodating severe volume changes during charge / discharge, thus providing high electrochemical performance in LIB and NIB applications. do. The hydroxyl group of NaCMC and the carboxylic acid group of PAA are responsible for the linkage with strongly-bonded hydrophilic BP and CNT. Thus, three forms, namely (1) hydrophilic BP and two binders (FIG. 4ii), (2) CNT and two binders (FIG. 4iii), and (3) two binders of each other (FIG. 4iv) There is a crosslinking. These additional bonds were re-formed through modified BP and their POC bonds as well as two distinct dehydration reactions of NaCMC and PAA binders. When the mixture of active material and binder was dried at 150 ° C. in vacuo, the esterification reaction occurred in the hydroxyl group of NaCMC, the carboxylic acid group of PAA, the -OH functional group of CNT, and H ₂ O adsorbed to BP powder. . In fact, as shown in FIG. 4iv, all components shared the —OH group in the dehydration process. As a result, the carefully selected composition formed a 3D cross-linked network containing the BP-CNT active material and the polymeric bicomponent binder in the prepared anode.

Consistent with the results of FIG. 5A, the FT-IR spectrum of PAA consisted of two carboxyl (-COOH) peaks at 1705 and 1411 cm ⁻¹ . These groups formed hydrogen bonds and the new bonds partially changed to dry carboxyl groups after vacuum drying at 150 ° C. Thus, the introduced hydrogen bonds and / or anhydrous carboxyl groups were responsible for the strong bonds in the PAA chain. Another clear -OCOOC- peak associated with the dehydration reaction was seen at about 1803 cm ^-1 , confirming the condensation reaction between the two carboxyl groups. No H ₂ O peak was observed and there was a -COC stretching vibration peak at about 1047 cm ⁻¹ . The NaCMC spectrum consisted of a peak at 1458 cm ⁻¹ associated with the —CH ₂ group, and two absorption peaks at 1622 and 1422 cm ⁻¹ as the stretching vibration of -COONa. Because of the formation of ester groups (-COO) in the binary c-NaCMC-PAA binder, a slight shift was observed in the C = O stretch band, which was at 1705 cm ^-1 compared to the COOH group of PAA at 1731 cm ^-1 Observed. In complex BPC4-c-NaCMC-PAA, the carboxyl groups at the open-terminal CNT tips and sidewalls were able to stably bind to the -OH group of NaCMC, which resulted in a new carboxylate (O = CO) stretching peak of the ester group ( 1580 cm ^{- 1} ). The same process took place on the carboxylic acid group of PAA to form a covalent ester bond with the carboxyl group of CNT. In addition, the broad -OH band between 3700 and 3200 cm ^-1 in the spectrum of BPC4-c-NaCMC-PAA was clearly weaker compared to the bare c-NaCMC-PAA binder, which was between the -OH functional groups of PAA and NaCMC. It is once again demonstrated that the binding of is weakened significantly by the cross-linking reaction with CNTs or during the adsorption on the hydrophilic BP to form strong POC linkages. FIG. 5B compares ¹³ C MAS-NMR results of BPC1-c-NaCMC-PAA and BPC4-c-NaCMC-PAA electrode materials, with the latter being primarily attributable to the esterification reaction between components. It also indicates that it has weakened sharply at. The reduction was more evident here compared to FIG. 5G without the binder. The two binders could also supply abundant —OH groups, so crosslinking was more apparent. In addition, local temperature increases during ball milling were the only cause for the occurrence of esterification reactions between the two modified BPs and the functionalized CNTs. As a result, it is reasonable to conclude that certain milling durations are necessary to form stable chemical bonds between the two active materials. Finally, the TG results (FIG. 5C) also showed an additional 2% weight loss in BPC4-c-NaCMC-PAA compared to BPC3-c-NaCMC-PAA, due to the rich crosslinking of the former. Thus, this new design maximizes the benefits of all components and is therefore expected to provide good electrochemical performance in the cell.

(4) LIB performance

All fabricated electrodes were evaluated for electrochemical properties for LIB application. All doses were measured based on the weight of BP because the dose of CNT was negligible in the potential window investigated in the present invention. To investigate the electrochemical reaction in detail during charging / discharging, 0.01 and 2.0 V vs. Cyclic voltammetry (CV) curves of BPC4-c-NaCMC-PAA in the voltage range of Li / Li ⁺ and 0.1 mV / s scan rate were obtained. The wide peak at 0.6 V observed in the cathode cycle of the first cycle was due to the activation of Li ⁺ upon insertion into the BP structure. Four reduction peaks were observed with cathode scans at 0.54, 0.69, 0.80 and 1.30 V in 2-5 cycles, corresponding to Li _x P (x = 1-3) formation. In the anode scan, three oxidation peaks were present at 1.03, 1.21 and 1.63 V due to the delithiation process. After the first cycle, the CV curve became fully reversible, suggesting stable electrochemical behavior during the cycling test. The peak at 1.21 V (vs. Li / Li ⁺ ) became stronger and slowly shifted toward the lower voltage from the first scan to the fifth scan, indicating an improved delithiation rate during cycling. According to the charge / discharge curves of the BPC4-c-NaCMC-PAA electrode material for LIB at a current density of 0.2 C, during the first discharge, an irreversible wide shoulder at about 1.25-0.95 V vs Li / Li ⁺ mainly This is due to the formation of a passive layer, ie solid-electrolyte intercalator (SEI). In addition, two or more sloped regions plus sloped plateaus were observed during the lithiation process with respect to the uptake of Li ⁺ in different reactions to form various Li _x P phases from BP. 6A shows the initial charge / discharge plateaus of all five complexes for LIB. The first charge / discharge of ˜760 / 1120, 1073/1380, 952/1235, 1768/1922 and 1503/1900 mAh / g was delivered by the BPC1, BPC2, BPC3, BPC4 and BPC5 complexes, respectively. In addition, the charge and discharge polarization in the potential curve decreased from 0.62 V in BPC1 to 0.50 V in BPC4, which corresponds to the formation of stable chemical bonds and crosslinks in the latter and is in full agreement with the previous discussion. Importantly, the BPC5 control sample showed higher polarization than BPC4, indicating the presence of inadequate POC binding and dehydration crosslinking compared to target BPC4. However, its initial charge and discharge capacity was higher than the BPC1-BPC3 samples. This difference seems to be due to the higher milling time than the other three samples, thus producing a purer BP powder (FIG. 2C) or a more functionalized and defective CNT, which together provided better initial charge / discharge performance.

6B compares the cycling performance of four composites for LIB at a current density of 0.2 C using BPC4-c-NaCMC-PAA, showing excellent cycle stability at 400 cycles and above. The initial discharge capacity was ˜1922 mAh / g and increased to ˜2094 mAh / g in the fourth cycle. After 400 cycles, the discharge capacity was maintained at 1681 mAh / g, corresponding to a capacity retention of 87.5% based on the first discharge capacity. As mentioned in the experimental details, the electrolyte contained fluoroethylene carbonate (FEC) to effectively stabilize the surface electrolyte interface (SEI) film. As shown in FIG. 6B, without FEC, the dose rapidly decreased. In addition, in contrast to BPC4, BPC5 was stable only in about 10-15 cycles, and its capacity rapidly decreased. The CE data of the same material as in FIG. 6B indicates that they all delivered a lower first discharge capacity than BPC4, mainly because there was no or insufficient compound bonds between the electrode components that could greatly improve the electrical contact therebetween. . Initial CEs for BPC1, BPC2, BPC3, BPC4 and BPC5 were 68.9, 77.8, 76.9, 92.0 and 79.1%, respectively. In all samples, the discharge and charge capacities were close to each other in later cycles, and CE reached over 99.8% in all four composites after 400 cycles. The high CE of BPC4 in the first cycle demonstrates that the electrochemical reaction between the first and last phases (BP and Li ₃ P, respectively) is nearly reversible. In addition, high CE also showed high conductivity of BPC4 compared to other samples.

6C shows the rate characteristic performance of four BPC1-BPC4 composites at various current densities. As the current density increases from 0.2 C to 4.5 C (= about 11700 mA / g), from 1950 to 1346 and 1100 to 299 mAh / g for BPC4-c-NaCMC-PAA and BPC1-c-NaCMC-PAA, respectively The discharge capacity continued to decrease. When the current density was switched back to 0.2 C, the discharge capacity rose back to values of 1713 and 1093 mAh / g, respectively, corresponding to about 90% of the initial capacity of BPC4. Initial capacity increased up to about the fourth cycle (FIGS. 6B, 6C) because of the modest decrease in SEI and charge transfer resistance, as indicated by electrochemical impedance spectroscopy (EIS) measurements.

The Nyquist plot of BPC4-c-NaCMC-PAA consists of a semicircle in the high / medium frequency region due to the charge transfer resistance (R _ct ) in the new cell and a straight line at low frequency. An additional semicircle appeared after cycling at high frequencies, which was associated with interfacial resistance in the SEI film (R _int ). In all plots the linear region is related to ion diffusion through the active material. R _int for the new cell was large, which decreased after 3 cycles. Additional cycling up to 100 cycles showed only a slight increase in resistance, which was mainly due to the formation of stable SEIs and the large influence of effective chemical bonding, which stabilized the electrode for long cycles. EIS results were consistent with cycle and velocity characteristic data and clearly accounted for capacity increase in the first few cycles. 6D demonstrates the excellent rate characteristics of BPC4-c-NaCMC-PAA at 1 C and 4.5 C in LIB for more than 300 cycles, with a discharge capacity of 1513 mAh / g after 100 cycles at 1 C and at 4.5 C. After an additional 200 cycles it reached 903 mAh / g. Finally, the performance of the 3D cross-linked bicomponent binder was compared with PVDF and PAA or NaCMC single binder up to 200 cycles. Comparing previous studies with current results on RP-CNTs and various BP-based materials in LIB, the cycle stability of the 3D c-NaCMC-PAA binder is significantly improved compared to commercial alternatives.

(5) NIB performance

Finally, target BPC4-c-NaCMC-PAA samples were evaluated in terms of electrochemical performance as anodes for NIB. The CV curves of this sample were plotted to elaborate the sodiumation / desodiation mechanism. 0.01-2.0 V vs. 0.1 mV / s for cycles 1-5 According to the CV curve in the voltage range of Na / Na ⁺ , wide and weak peaks appeared at about 0.6 V in the first cathode scan because of the formation of the SEI layer. A new peak was observed at about 0.9 V in subsequent scans because of the initial sodiumation of BP. Two or more cathode peaks centered at about 0.35 and 0.19 V in the range 0.8-0.01 V were observed, due to the formation of Na ⁺ insertion and Na _x P (1 <x ≦ 3). These peaks gradually shifted to the lower voltage range and remained there after 5 cycles. The potential shift can be explained in terms of the activation step, which confirmed the progressively improved sodiumation rate by slightly increasing the peak intensity from the third to fifth scans. Peaks located at 0.55, 0.67 and 1.43 V during the first anion scan also appeared in later scans. These peaks mostly corresponded to staged Na ⁺ de-insertion from the fully filled Na ₃ P phase. At 0.67 V the peak current was improved and its potential shifted to a slightly lower voltage from the first to fifth scans, indicating an improved rate of de-sodiumation during cycling.

The charge / discharge profile of the BPC4-c-NaCMC-PAA complex in the first to fifth cycles showed a stepwise sodiumation, ie a sharp gradient at about 1.25-0.48 V vs Na / Na ⁺ , then about 0.48-0.1 V Plateau with a slight slope at, finally a small slope at 0.1 to 0.01 V. 6E shows the cycle performance of BPC4-c-NaCMC-PAA for NIB half-cell. The first discharge capacity was about 2073 mAh / g at 0.2 C and reached 1560 mAh / g after 200 cycles (capacity retention = 75.2% compared to the first cycle). Initial CE was 87.7%. 6F shows the rate properties of BPC4-c-NaCMC-PAA electrode material from 0.2 C to 4.5 C at high speeds. The discharge capacities shown were about 2060 (0.2 C), 1653 (0.3 C), 1409 (0.7 C), 1200 (1.5 C), 810 (2 C), 609 (3 C) and 441 (4.5 C) mAh / g. . Surprisingly, the BPC4-C-NaCMC-PAA electrode successfully exhibited a very large reversible capacity (441 mAh / g) even at very high current densities of 11.7 A / g. After changing the speed back to 0.2 C after 42 cycles, the capacity returned to 1656 mAh / g, which was almost identical to that of the second cycle (1753 mAh / g) at the same speed. Thus, the charge / discharge process at the designed electrode was completely reversible even at high current densities. More importantly, as shown in FIG. 6G, very stable fast cycle performance was observed at 1 C and 2 C for at least 100 cycles, respectively. The capacity reached 1050 mAh / g from 1270 after 100 cycles at 1 C. An additional 100 cycles at 2 C resulted in a final discharge capacity of 700 mAh / g. These results were also compared with RP-CNTs and various BP-based materials. This extremely fast performance may be due to the strong and stable 3D electrode framework with excellent connectivity and electrical conductivity, along with extremely small BP nanocrystals that shorten the diffusion path for Na ions during charge / discharge.

In order to explain the kinetics in more detail during the electrochemical test, EIS data of BPC4-c-NaCMC-PAA for NIB were obtained in a discharge state at 2-0.01 V (vs Na ⁺ / Na). The Nyquist plot again showed that the change in the diameter of the semicircle region at high / medium frequencies was very negligible after the 100th cycle, and the remarkable cycle and velocity characteristics of BPC4, mainly due to high electrical conductivity, were stable SEI, a special 3D binary binder structure , And some forms of strong chemical bonds formed, all of which prevented electrode failure.

According to SEM images of pre-fabricated BPC4-c-NaCMC-PAA and electrodes tested for 400 and 200 cycles in LIB and NIB cells, respectively, the cycled LIB electrode showed small cracks at low resolution, while NIB Cracks in the electrodes were more apparent. The integrated form in both cells demonstrated well-preserved electrode structure after a long cycle at 0.2 C. Elemental mapping analysis of the cycled BPC4-c-NaCMC-PAA electrode for LIB showed a uniform distribution of P and C in the electrode after at least 400 cycles.

3. Conclusion

In short, the present invention successfully synthesized BP-CNT composites through surface oxygen adsorption-assisted crosslinking process for the first time, and applied to fabricate anodes for LIB and NIB using strong, cross-linked bicomponent polymeric binders. It was. This anode showed surprisingly high electrochemical performance in both applications, mainly due to the strong 3D cross-linked network. The root cause of this good electrochemical performance was the stable chemical bonding between hydrophilic BP powder, functionalized CNTs and binders formed during ball-milling and electrode fabrication processes. The parameters affecting the binding of the components were thoroughly investigated and the possible mechanisms were evaluated to reveal two forms of strong and robust P-O-C binding and dehydration crosslinking. This result will therefore provide important insights for further improving the electrochemical performance of BP-based electrode materials in various energy applications.

Claims (26)

Milling red phosphorus to synthesize black phosphorus;
Mixing the synthesized black phosphorus and carbon nanotubes while being exposed to air;
Milling the air-exposed black lean and carbon nanotube mixture,
Air exposure time is 20-60 minutes,
Through air exposure, the surface of the black lean was oxidized to hydrophilically modify the black lean, which was hydrophobic.
Through air exposure, black phosphorus contains hydrophilic and defective surface layers and lattice defects and adsorbed oxygen atoms,
Through air exposure, phosphorus pentoxide is formed in black phosphorus,
Phosphorous pentoxide reacts with water to form phosphoric acid, thereby functionalizing the carbon nanotubes on the surface thereof. The method of claim 1,
A method for producing a black phosphorus-carbon nanotube composite, characterized in that the red phosphorus is milled in an inert gas atmosphere in a black phosphorus synthesis step. The method of claim 2,
Inert gas is argon, milling method of producing a black lean-carbon nanotube composite, characterized in that performed using a planetary ball mill. The method of claim 3,
Ball-to-powder (BPR) mass ratio is 40 ± 10: 1, milling speed is 450 ± 100 rpm, milling time is 10 to 80 hours, characterized in that the manufacturing method of the black lean-carbon nanotube composite. The method of claim 1,
The mixing ratio of black phosphorus and carbon nanotubes is a weight ratio of 5 to 9: 1 to 5, characterized in that the manufacturing method of the black phosphorus-carbon nanotube composite. delete The method of claim 1,
Use a planetary ball mill in the milling step of the black phosphorus and carbon nanotube mixtures, with a ball-to-powder (BPR) mass ratio of 20 ± 10: 1, milling speed of 300 ± 100 rpm, and milling time of 10 to 80 Method for producing a black lean-carbon nanotube complex, characterized in that time. The method of claim 1,
Through milling, amorphous red phosphorus is converted to crystalline black phosphorus, characterized in that the method for producing a black phosphorus-carbon nanotube complex. The method of claim 1,
The content of the crystalline phase in the synthesized black lean is a method for producing a black lean-carbon nanotube complex, characterized in that more than 60%. delete The method of claim 1,
A method for producing a black lean-carbon nanotube composite, characterized in that the hydrophilic surface-modified black lean forms a strong POC bond with the carbon nanotube. delete delete delete The method of claim 1,
Through milling, black phosphorus-weakens sp ² -type carbon of carbon nanotubes, forms lattice points, adsorption atoms, edges and gaps in carbon nanotubes, and increases the active sites of carbon nanotubes. Method for producing a carbon nanotube composite. The method of claim 1,
The D-to-G band (I _D / I _G ratio) of the milled carbon nanotubes is 1.3 or more, the G-band frequency is 1591 cm ^-1 or more, and the percentage of sp ² -type carbon is 80% or less. Method of producing a black lean-carbon nanotube composite. An electrode using a black phosphorus-carbon nanotube composite, a conductive agent and a binder prepared according to claim 1 as an active material,
The binder is a two-component binder,
Black phosphorus binds to the binder through POC chemical bonding and dehydration crosslinking,
An electrode characterized in that crosslinking is formed between the carbon nanotubes and the binder and between the binders. delete The method of claim 17,
The binder comprises at least two or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, and poly (acrylic acid). The method of claim 17,
An electrically conductive agent is carbon black. The method of claim 17,
The mixing ratio of the composite: conductor: binder is 70 ± 10: 15 ± 10: 15 ± 10 as weight ratio. delete delete The method of claim 17,
The electrode is used as an anode of a lithium ion battery or a sodium ion battery. The method of claim 24,
In a lithium ion battery, the electrode has a discharge capacity of 1600 mAh / g or more after 400 cycles at a current density of 0.2 C and maintains a capacity of 80% or more based on the first discharge capacity. The method of claim 24,
In a sodium ion battery, the electrode has a discharge capacity of 1500 mAh / g or more after 200 cycles at a current density of 0.2 C and maintains a capacity of 70% or more based on the first discharge capacity.

Images