Composite negative electrode material, and preparation method therefor and use thereof

Abstract

A composite negative electrode material, and a preparation method therefor and the use thereof. The composite negative electrode material comprises elemental phosphorus, an electrically conductive carbon material, and a phosphate. The mass ratio of elemental phosphorus, the electrically conductive carbon material and the phosphate is 4:x:y, wherein x+y=6, and x and y are both greater than 0. By compounding elemental phosphorus, the electrically conductive carbon material and the phosphate at a specific ratio to prepare the composite negative electrode material, the combined effect of the three endows the composite negative electrode material with excellent reaction kinetics and structural stability characteristics, such that a prepared battery has a high capacity, good cycling stability and good rate capacity.

Description

A composite negative electrode material and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a composite negative electrode material and a preparation method and application thereof. Background Art

[0002] At present, lithium-ion batteries usually use phosphorus as the negative electrode material, especially black phosphorus. Black phosphorus (BP) has a theoretical capacity of up to 2600mAh / g, a lithium insertion potential of about 0.7V, and a lithium ion migration energy barrier of 0.08eV. It is an ideal choice as a fast-charging negative electrode material for lithium-ion batteries. However, the low bulk ion / electronic conductivity of phosphorus, the slow reaction kinetics caused by the complex phase transitions of alloying and dealloying processes, severe volume expansion, and poor environmental stability have hindered its practical application. At present, there have been studies on the use of conductive polymers to coat phosphorus-carbon composite materials, the use of porous black phosphorene self-supporting negative electrode materials, and the synthesis of phosphorus negative electrodes by magnetron sputtering. There are also studies on the preparation of phosphorus-metal organic framework composite materials. However, the above studies still have problems with complex synthesis methods or low production efficiency, and have never been able to completely solve the problems of slow reaction kinetics, severe volume expansion, and poor environmental stability of phosphorus materials, which in turn affect the cycle performance and rate performance of lithium-ion batteries.

[0003] Therefore, there is an urgent need to provide a composite negative electrode material with excellent reaction kinetics and structural stability, and the prepared battery has high capacity, good cycle stability and rate performance.

[0004] Summary of the Invention

[0005] The present invention aims to address one or more of the above-mentioned technical problems in the prior art, at least by providing a beneficial alternative or creating a suitable solution. Specifically, the present invention provides a composite anode material having excellent reaction kinetics and structural stability, and the resulting battery has high capacity, good cycle stability, and good rate performance.

[0006] The inventive concept of the present invention is as follows: The composite negative electrode material of the present invention includes phosphorus, a conductive carbon material, and a phosphate; the mass ratio of the phosphorus, the conductive carbon material, and the phosphate is 4:x:y; wherein x+y=6, and both x and y are greater than 0. The present invention prepares the composite negative electrode material by compounding the phosphorus, the conductive carbon material, and the phosphate in a specific ratio. The zinc phosphate in the composite negative electrode material is amorphous, which can reduce the problems of slow reaction kinetics and severe volume expansion caused by the complex phase transformation of the phosphorus during the alloying and dealloying processes. The conductive carbon material can improve the conductivity of the composite negative electrode material and form PC / PCO bonds with the phosphorus, thereby improving the structural stability of the composite negative electrode material. The phosphorus, the conductive carbon material, and the phosphate work together to give the composite negative electrode material excellent reaction kinetics and structural stability, thereby resulting in a high capacity, good cycle stability, and high rate performance for the prepared battery.

[0007] Therefore, a first aspect of the present invention provides a composite negative electrode material.

[0008] Specifically, the composite negative electrode material includes phosphorus, a conductive carbon material and phosphate; the mass ratio of the phosphorus, the conductive carbon material and the phosphate is 4:x:y; wherein x+y=6, and x and y are both greater than 0.

[0009] Specifically, the composite negative electrode material is amorphous.

[0010] Preferably, the phosphorus element is selected from at least one of black phosphorus and red phosphorus.

[0011] Preferably, the phosphate is selected from at least one of zinc phosphate, lithium phosphate and aluminum phosphate.

[0012] Preferably, the phosphate is amorphous.

[0013] Preferably, the conductive carbon material is selected from at least one of Super P Li, acetylene black, graphite, hard carbon, soft carbon, and Ketjen black.

[0014] Specifically, the Super P Li is a super dense and highly conductive carbon black.

[0015] Preferably, the value of y is 0.45≤y≤5.5, and / or the value of x is 0.5≤x≤5.55; further preferably, the value of y is 0.5≤y≤5; and / or the value of x is 1≤x≤5.5.

[0016] Preferably, the composite negative electrode material is spherical, and the particle size of the composite negative electrode material is 4.5-9 μm; further preferably, the particle size of the composite negative electrode material is 5-8 μm.

[0017] The second aspect of the present invention provides a method for preparing the composite negative electrode material described in the first aspect of the present invention.

[0018] Specifically, the method for preparing the composite negative electrode material comprises the following steps:

[0019] The phosphorus element, the conductive carbon material and the phosphate are mixed to obtain a mixture; and the mixture is ball-milled to obtain the composite negative electrode material.

[0020] Preferably, grinding balls are used for ball milling; the mass ratio of the grinding balls to the mixture is 45-100:1; further preferably, the mass ratio of the grinding balls to the mixture is 50-90:1.

[0021] Preferably, the grinding balls include steel balls A and steel balls B.

[0022] Preferably, the ratio of the number of the steel balls A to the number of the steel balls B is 1:(0.9-3.5); further preferably, the ratio of the number of the steel balls A to the number of the steel balls B is 1:(1-3).

[0023] Preferably, the diameter of the steel ball A is 8-12 mm, and the diameter of the steel ball B is 4-6 mm; further preferably, the diameter of the steel ball A is 9-11 mm, and the diameter of the steel ball B is 4.5-5.5 mm; even further preferably, the diameter of the steel ball A is 10 mm, and the diameter of the steel ball B is 5 mm.

[0024] Preferably, the ball milling speed is 700-900 r / min, and the ball milling time is 5.5-8.5 h; further preferably, the ball milling speed is 750-850 r / min, and the ball milling time is 6-8 h.

[0025] Specifically, the ball milling is performed in a ball milling jar. During the ball milling, the ball milling jar is operated and stopped alternately, and the ball milling time is the actual operating time.

[0026] Preferably, when the phosphorus element is black phosphorus, the method for preparing black phosphorus comprises the following steps:

[0027] The black phosphorus is prepared by ball milling red phosphorus.

[0028] Preferably, the ball milling is performed using grinding balls, and the mass ratio of the grinding balls to the red phosphorus is (25-65):1; further preferably, the mass ratio of the grinding balls to the red phosphorus is (30-60):1.

[0029] Preferably, the grinding balls include steel balls A and steel balls B.

[0030] Preferably, the ratio of the number of the steel balls A to the number of the steel balls B is 1:(0.9-3.5); further preferably, the ratio of the number of the steel balls A to the number of the steel balls B is 1:(1-3).

[0031] Preferably, the diameter of the steel ball A is 8-12 mm, and the diameter of the steel ball B is 4-6 mm; further preferably, the diameter of the steel ball A is 9-11 mm, and the diameter of the steel ball B is 4.5-5.5 mm; even further preferably, the diameter of the steel ball A is 10 mm, and the diameter of the steel ball B is 5 mm.

[0032] Preferably, the ball milling speed is 700-900 r / min, and the ball milling time is 12-32 h; further preferably, the ball milling speed is 750-850 r / min, and the ball milling time is 13-30 h.

[0033] Specifically, the ball milling is performed in a ball milling jar. During the ball milling, the ball milling jar is operated and stopped alternately, and the ball milling time is the actual operating time.

[0034] A third aspect of the present invention provides a negative electrode.

[0035] Specifically, the negative electrode includes a coating formed by the composite negative electrode material described in the first aspect of the present invention.

[0036] Preferably, the coating layer also includes a conductive agent and a binder.

[0037] Preferably, the conductive agent is acetylene black.

[0038] Preferably, the binder includes at least one of styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC); more preferably, the binder includes SBR and CMC.

[0039] Preferably, the mass ratio of the SBR to the CMC is 0.8-1.2:1; further preferably, the mass ratio of the SBR to the CMC is 0.9-1.1:1; even further preferably, the mass ratio of the SBR to the CMC is 1:1.

[0040] Preferably, the mass ratio of the composite negative electrode material, the conductive agent and the binder is 7: (1.0-2.0): (1.0-2.0); further preferably, the mass ratio of the composite negative electrode material, the conductive agent and the binder is 7: (1.3-1.7): (1.3-1.7); further preferably, the mass ratio of the composite negative electrode material, the conductive agent and the binder is 7: 1.5: 1.5.

[0041] Preferably, the method for preparing the negative electrode comprises the following steps:

[0042] The composite negative electrode material, a conductive agent, and a binder are mixed to obtain a mixed solution, the mixed solution is coated on a current collector, and the mixture is dried to obtain the negative electrode.

[0043] Preferably, the current collector is selected from copper foil.

[0044] A fourth aspect of the present invention provides a battery.

[0045] Specifically, the battery includes a positive electrode, an electrolyte, and the negative electrode described in the third aspect of the present invention.

[0046] Preferably, the battery is a lithium-ion battery.

[0047] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0048] (1) The present invention adopts a strategy of combining phosphorus, conductive carbon material and phosphate in a specific proportion to prepare a composite negative electrode material. The zinc phosphate in the composite negative electrode material is amorphous, which can reduce the problems of slow reaction kinetics and severe volume expansion caused by the complex phase change of phosphorus during alloying and dealloying; the conductive carbon material can improve the conductivity of the composite negative electrode material, and the conductive carbon material can form PC / PCO bonds with phosphorus to improve the structural stability of the composite negative electrode material; the phosphorus, conductive carbon material and phosphate work together to make the composite negative electrode material have excellent reaction kinetics and structural stability, thereby making the prepared battery have high capacity, good cycle stability and rate performance, and fast charging performance. The 1C capacity can reach 903mAh / g, and the 500-cycle cycle retention rate is 81%. The 4C capacity can be 590mAh / g, and the 300-cycle retention rate is 86%.

[0049] (2) The present invention adopts the ball milling method to synthesize the composite negative electrode composite material, which has a simple preparation process. By adjusting the ball milling speed, ball milling time and ball-to-material ratio, the formation of PC / PCO bonds can be controlled to achieve the preparation of amorphous composite negative electrode materials, which is low in cost and convenient for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG1 is an SEM and mapping image of the BP@C@ZPO composite negative electrode material of Example 1 of the present invention;

[0051] FIG2 is an XRD diagram of the composite negative electrode materials of Example 1 and Example 2 of the present invention;

[0052] FIG3 is an infrared spectrum and a Raman spectrum of the composite negative electrode materials of Example 1 and Comparative Examples 3 and 4 of the present invention;

[0053] FIG4 is a UV spectrogram of a lithium polyphosphide solution, a lithium polyphosphide solution and a zinc phosphate solution;

[0054] FIG5 is a graph showing the XPS test results of the composite negative electrode materials of Example 1 and Comparative Examples 3 and 4 of the present invention;

[0055] FIG6 is a graph showing the reaction kinetics test results of Application Example 1, Comparative Application Example 3, and Comparative Application Example 4 of the present invention;

[0056] FIG7 is a graph showing the CV test results of Application Example 1, Comparative Application Example 3, and Comparative Application Example 4 of the present invention;

[0057] FIG8 is a pseudocapacitance fitting diagram of Application Example 1, Comparative Application Example 3, and Comparative Application Example 4 of the present invention;

[0058] FIG9 is a graph showing the electrochemical performance of Application Example 1, Comparative Application Example 3, and Comparative Application Example 4 of the present invention;

[0059] FIG10 is a graph showing the electrochemical performance of Application Example 2 of the present invention, Comparative Application Example 1, and Comparative Application Example 2;

[0060] FIG11 is a graph showing the electrochemical performance of Gr and Si-C in the control group and Application Example 1 of the present invention;

[0061] FIG12 is a graph showing the structural stability test results of the composite negative electrode materials of Example 1, Comparative Example 3, and Comparative Example 4 of the present invention;

[0062] FIG13 is a graph showing the volume expansion test results of the battery electrodes of Application Example 1, Comparative Application Example 3, and Comparative Application Example 4 of the present invention. DETAILED DESCRIPTION

[0063] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0064] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0065] Example 1.

[0066] A black phosphorus / conductive carbon material / zinc phosphate composite negative electrode material (BP@C@ZPO) includes 0.4g of black phosphorus, 0.3g of zinc phosphate, and 0.3g of conductive carbon material Super P Li.

[0067] A method for preparing a BP@C@ZPO composite negative electrode material comprises the following steps:

[0068] Black phosphorus, Super P Li and zinc phosphate were placed in a ball mill to obtain a mixture, and then 11 steel balls with a diameter of 10 mm and 11 steel balls with a diameter of 5 mm were added. The mass ratio of the steel balls to the mixture was 50:1. The ball mill was sealed in a glove box filled with argon so that the material was ball milled in an inert gas. The ball milling speed was 800 r / min. During ball milling, the process was run for 3 minutes and stopped for 15 minutes, alternating for a total of 6 hours to obtain the BP@C@ZPO composite negative electrode material.

[0069] The method for preparing black phosphorus comprises the following steps:

[0070] 2.2 g of red phosphorus was placed in an 80 mL ball mill, and 20 steel balls with a diameter of 10 mm and 20 steel balls with a diameter of 5 mm were added. The mass ratio of steel balls to red phosphorus was 40:1. The ball mill was sealed in an argon-filled glove box so that the material was ball milled in an inert gas. The ball mill speed was 800 r / min, and the process was run for 3 minutes and stopped for 15 minutes, alternating for a total running time of 16 hours to produce black phosphorus.

[0071] Example 2.

[0072] A black phosphorus / conductive carbon material / lithium phosphate composite negative electrode material (BP@C@LPO) includes 0.4g of black phosphorus, 0.1g of lithium phosphate, and 0.5g of conductive carbon material acetylene black.

[0073] A method for preparing a BP@C@LPO composite negative electrode material comprises the following steps:

[0074] Black phosphorus, acetylene black and lithium phosphate were placed in a ball mill to obtain a mixture, and then 13 steel balls with a diameter of 10 mm and 14 steel balls with a diameter of 5 mm were added. The mass ratio of the steel balls to the mixture was 60:1. The ball mill was sealed in a glove box filled with argon so that the material was ball milled in an inert gas. The ball milling speed was 800 r / min, and the process was repeated for 3 minutes and 15 minutes, alternating for a total of 6 hours to obtain the BP@C@LPO composite negative electrode material.

[0075] The preparation method of black phosphorus is the same as that in Example 1.

[0076] Example 3.

[0077] A black phosphorus / conductive carbon material / aluminum phosphate composite negative electrode material includes 0.4g of black phosphorus, 0.3g of aluminum phosphate, and 0.3g of conductive carbon material graphite.

[0078] A method for preparing a black phosphorus / conductive carbon material / aluminum phosphate composite negative electrode material comprises the following steps:

[0079] Black phosphorus, graphite and aluminum phosphate were placed in a ball mill to obtain a mixture, and then 15 steel balls with a diameter of 10 mm and 18 steel balls with a diameter of 5 mm were added. The mass ratio of the steel balls to the mixture was 70:1. The ball mill was sealed in a glove box filled with argon so that the material was ball milled in an inert gas. The ball milling speed was 800 r / min, and the process was repeated for 3 minutes and 15 minutes, alternating for a total of 6 hours to obtain a black phosphorus / conductive carbon material / aluminum phosphate composite negative electrode material.

[0080] The method for preparing black phosphorus comprises the following steps:

[0081] 2.2 g of red phosphorus was placed in an 80 mL ball mill, and 29 steel balls with a diameter of 10 mm and 29 steel balls with a diameter of 5 mm were added. The mass ratio of steel balls to red phosphorus was 60:1. The ball mill was sealed in an argon-filled glove box so that the material was ball milled in an inert gas. The ball mill speed was 800 r / min, and the process was run for 3 minutes and stopped for 15 minutes, alternating for a total running time of 12 hours to produce black phosphorus.

[0082] Comparative Example 1

[0083] The only difference between Comparative Example 1 and Example 2 is that an equal amount of Si is used to replace the black phosphorus in Example 2. The rest is the same as Example 2, and is denoted as Si@C@LPO.

[0084] In addition, a reference electrode control group was also set up in Comparative Example 1. The only difference between the reference electrode control group and Comparative Example 1 was that zinc phosphate was not added to the control group. Other conditions were the same as Comparative Example 1 and were recorded as Si@C.

[0085] Comparative Example 2

[0086] The only difference between Comparative Example 2 and Example 2 is that an equal amount of aluminum oxide is used to replace the lithium phosphate in Example 2, and the rest is the same as Example 2.

[0087] Comparative Example 3

[0088] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses an equal amount of conductive carbon material Super P Li to replace zinc phosphate, that is, Comparative Example 3 does not contain zinc phosphate, the conductive carbon material is 0.6g, and the rest is the same as Example 1, recorded as 40BP+SP.

[0089] Comparative Example 4

[0090] The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 uses an equal amount of black phosphorus to replace zinc phosphate, that is, Comparative Example 4 does not contain zinc phosphate, and the amount of black phosphorus is 0.7 g. Other components are the same as Example 1, and are recorded as 70BP+SP.

[0091] Application Example 1

[0092] A button half-cell is disclosed. The composite negative electrode material of Example 1, acetylene black, and a binder (the mass ratio of SBR and CMC is 1:1, the mass fraction of the CMC solution is 1.5%, and the mass fraction of the SBR solution is 45%) are mixed in a mass ratio of 7:1.5:1.5, and magnetic stirring is performed to uniformly mix the mixture to obtain a mixture. The mixture is then coated on a copper foil, placed in a drying oven, pre-dried at 60°C for 2 hours, and then transferred to a vacuum drying oven and dried at 60°C for 8 hours to obtain a negative electrode. The dried negative electrode is pressed and punched into a 12 mm diameter disc for subsequent testing. Lithium metal and a PP separator are used as a counter electrode and a separator, respectively. 1M LiPF6 is dissolved in a solvent with a DEC:EC ratio of 1:1, and 10% FEC and 1% VC are added as film-forming additives. The button half-cell (CR2032) is assembled in an Ar atmosphere-filled glove box to obtain the button half-cell.

[0093] Application Example 2

[0094] The only difference between Application Example 2 and Application Example 1 is that the composite negative electrode material of Example 2 is used, and the rest is the same as Application Example 1.

[0095] Application Example 3

[0096] The only difference between Application Example 3 and Application Example 1 is that the composite negative electrode material of Example 3 is used, and the rest is the same as Application Example 1.

[0097] Comparative Application Example 1

[0098] The difference between Comparative Example 1 and Application Example 2 is that the composite negative electrode material of Comparative Example 1 is used, and the rest is the same as Application Example 2.

[0099] Comparative Application Example 2

[0100] The difference between Comparative Example 2 and Application Example 2 is that the composite negative electrode material of Comparative Example 2 is used, and the rest is the same as Application Example 2.

[0101] Comparative Application Example 3

[0102] The difference between Comparative Example 3 and Application Example 1 is that the composite negative electrode material of Comparative Example 3 is used, and the rest is the same as Application Example 1.

[0103] Comparative Application Example 4

[0104] The difference between Comparative Example 4 and Application Example 1 is that the composite negative electrode material of Comparative Example 4 is used, and the rest is the same as Application Example 1.

[0105] Performance Testing

[0106] 1.SEM testing

[0107] The BP@C@ZPO composite negative electrode material prepared in Example 1 was subjected to SEM testing. The SEM image and Mapping image are shown in Figure 1, wherein Figure 1(a) is an SEM image, Figure 1(b)(c)(e)(f) are Mapping images of C, O, P, and Zn elements, respectively, and Figure 1(d) is an element Mapping image.

[0108] As shown in FIG1 , the composite negative electrode material of Example 1 is an irregular sphere composed of secondary particles, and the C / O / P / Zn elements are evenly distributed on the surface of the material, indicating that the elements are evenly mixed.

[0109] 2.XRD test

[0110] The composite negative electrode materials prepared in Example 1 and Example 2 were subjected to XRD testing, and the test results are shown in Figure 2. Figure 2(a) is the XRD spectrum of the composite negative electrode material of Example 1, and Figure 2(b) is the XRD spectrum of the composite negative electrode material of Example 2. In Figure 2(a), SP represents a conductive carbon material, BP represents black phosphorus, ZPO represents zinc phosphate, and BP@C@ZPO represents the composite negative electrode material of Example 1; the abscissa 2θ (degree) of Figures 2(a) and (b) both represent the diffraction angle 2θ (°), and the ordinate Intensity represents the diffraction intensity.

[0111] As can be seen from FIG2 , the composite negative electrode material obtained after ball milling is an amorphous substance, which is conducive to alleviating the problem of volume expansion of the material during the cycle.

[0112] 3. Infrared spectroscopy and Raman spectroscopy testing

[0113] The composite negative electrode materials prepared in Example 1, Comparative Example 3 and 4 were subjected to infrared spectroscopy and Raman spectroscopy tests, respectively. The infrared spectra and Raman spectra are shown in Figures 3(a) and (b), respectively, where BP@C@ZPO, 40BP+SP, 70BP+SP, and BP represent the composite negative electrode materials and black phosphorus of Example 1, Comparative Example 3, and Comparative Example 4, respectively; the horizontal axis Wavenumber (cm -1 ) represents wavelength, and the vertical axis Intensity represents intensity; the horizontal axis Raman shift (cm -1 ) represents the Raman shift (wave number), and the vertical axis Intensity represents the intensity; in Figure 3(b), G band and D band represent the G peak and D peak, respectively.

[0114] As can be seen from Figure 3(a), in addition to black phosphorus, 40BP+SP, 70BP+SP, and BP@C@ZPO all contain POC bonds, that is, the composite negative electrode materials of Example 1, Comparative Example 3, and Comparative Example 4 all contain POC bonds. As can be seen from Figure 3(b), the ID / IG ratio of the D and G peaks in 70BP+SP is the largest (1.143), that is, the composite negative electrode material sample in Comparative Example 4 has the most defects, indicating that increasing the black phosphorus content will bring more defects, which is not conducive to improving the electrochemical performance of the material.

[0115] 4. Zinc phosphate adsorption test

[0116] During the charge and discharge process, black phosphorus undergoes an alloying reaction to form lithium polyphosphide, which reduces the utilization rate of phosphorus. To verify the adsorption effect of zinc phosphate on lithium polyphosphide, ultraviolet spectral absorption tests were performed on lithium polyphosphide and lithium polyphosphide + zinc phosphate solutions. The preparation process of the lithium polyphosphide solution is as follows: 1.54g of biphenyl is dissolved in 10mL of THF (tetrahydrofuran), 0.01mol of lithium block is added, and the reaction is stirred to produce a 1M lithium biphenyl solution; then 200mg of red phosphorus is added and the reaction is carried out at room temperature in a glove box until the reaction is complete; the completely reacted solution is centrifuged, and the solid is dissolved in DEC (diethyl carbonate) to obtain the lithium polyphosphide solution. The preparation process of the lithium polyphosphide + zinc phosphate solution is as follows: 3mL of the lithium polyphosphide prepared above is placed in a 5mL glass bottle, and then 0.1g of zinc phosphate solution is added.

[0117] The UV spectrum test results are shown in Figure 4. Figure 4(a) is the UV spectrum absorption spectrum; Figure 4(b) is the optical photograph after adsorption. The horizontal axis Wavelength (nm) in Figure 4(a) represents the wavelength (nanometers), and the vertical axis Absorbance represents the absorbance.

[0118] As can be seen in Figure 4, after the addition of zinc phosphate, lithium polyphosphide is absorbed and the absorption peak at 320 nm disappears, indicating that zinc phosphate has an adsorption effect on lithium polyphosphide. After adsorption, the solution appears white. This indicates that the composite negative electrode material prepared in Example 1 of the present invention, because it contains zinc phosphate, can absorb lithium polyphosphide formed by black phosphorus alloying during the charge and discharge process of the battery prepared therefrom, reducing phosphorus loss and improving phosphorus utilization, thereby improving the battery's rate performance and cycle performance.

[0119] 5.XPS test

[0120] XPS tests were performed on the composite negative electrode materials prepared in Example 1, Comparative Examples 3 and 4, where BP@C@ZPO, 40BP+SP and 70BP+SP represent the composite negative electrode materials of Example 1, Comparative Example 3 and Comparative Example 4, respectively. The results are shown in FIG5 , where FIG5(a), (b) and (c) are the C1s spectrum, P2p spectrum and O1s spectrum, respectively, where the horizontal axis Binding energy (eV) represents the binding energy (electron volts), the oxygenated deposited component in FIG5(c) represents the oxidized deposited component, and POx represents the oxidized phosphorus compound. In addition, in FIG5(a), the upper, middle and lower figures represent the C1s spectra of BP@C@ZPO, 70BP+SP and 40BP+SP, respectively; in FIG5(b), the upper, middle and lower figures represent the P2p spectra of BP@C@ZPO, 70BP+SP and 40BP+SP, respectively.

[0121] As shown in Figure 5, the energy generated by high-energy ball milling allows the formation of stable P-C bonds between black phosphorus and the conductive carbon material (Figure 5a). The P-C bond contents in the 40BP+SP / 70BP+SP / BP@C@ZPO samples are 89%, 45%, and 65%, respectively. ZPO in the BP@C@ZPO sample makes a significant contribution to the P-C bond. Furthermore, the BP@C@ZPO sample has the lowest surface oxygen-containing species content, accounting for only 25%, when exposed to air. This is compared to 67% and 62% for the 40BP+SP and 70BP+SP samples, respectively, indicating that the BP@C@ZPO composite anode material prepared in Example 1 has good air stability.

[0122] 6. Reaction kinetics test

[0123] Reaction kinetics tests were performed on the batteries prepared in Example 1, Comparative Example 3, and Comparative Example 4, where BP@C@ZPO, 40BP+SP, and 70BP+SP represent the composite negative electrode materials of Example 1, Comparative Example 3, and Comparative Example 4, respectively. The results are shown in FIG6 , where FIG6( a ), ( b ), and ( c ) are dQ / dV plots of Comparative Example 3, Comparative Example 4, and Example 1, respectively; FIG6( d ) is a lithium ion diffusion coefficient plot of Comparative Example 3, Comparative Example 4, and Example 1; FIG6( e ) is an impedance plot at different temperatures for Example 1; and FIG6( f ) is an Arrhenius plot for Example 1. In FIG6( a ), ( b ), and ( c ), the horizontal axis Voltage (V) represents voltage (volts), the vertical axis dQ / dV represents battery capacity change, the SEI formation in FIG6( c ) represents SEI formation, and the horizontal axis Voltage (V vs.Li + / Li) represents the voltage (relative to the potential of lithium ions / metal lithium), the vertical axis Log(DLi + ,cm 2 s -1 ) represents the lithium ion diffusion coefficient; in Figure 6(e), the horizontal coordinate Z′(ohm) represents the real part of the impedance, the vertical coordinate -Z″(ohm) represents the imaginary part of the impedance, and fitted represents fitting; in Figure 6(e), the horizontal coordinate 1000T(K -1 ) represents the reciprocal of absolute temperature, the vertical coordinate is lnR ct -1 (Ω -1 ) represents the logarithm of the reciprocal of the charge transfer resistance during the discharge process.

[0124] As shown in Figure 6, the 40BP+SP composite negative electrode material of Comparative Application Example 3 has the highest content of conductive carbon material, resulting in the formation of a large amount of SEI during the electrochemical cycle, insufficient black phosphorus reaction, and unclear redox peaks (Figure 6(a)). In contrast, the 70BP+SP composite negative electrode material of Comparative Application Example 4 has a high black phosphorus content, high redox activity but also instability, with a significant decrease in peak intensity after 30 cycles (Figure 6(b)). The BP@C@ZPO composite negative electrode material of Application Example 1 has a stable peak intensity during the electrochemical activation process, demonstrating excellent electrochemical stability (Figure 6(c)). Calculation of the lithium ion diffusion coefficient using GITT shows that the BP@C@ZPO composite negative electrode material of Application Example 1 has a faster lithium ion migration rate during the reaction (Figure 6(d)). The activation energy calculated from the charge transfer resistance in EIS (Figure 6(e), (f)) is only 44.1 kJ / mol, which is lower than the 50-55 kJ / mol of materials such as graphite, indicating that the BP@C@ZPO composite negative electrode material prepared in Example 1 has faster reaction kinetics.

[0125] 7.CV test

[0126] CV tests were performed on the batteries prepared in Example 1, Comparative Example 3 and 4, where BP@C@ZPO, 40BP+SP and 70BP+SP represent the composite negative electrode materials of Example 1, Comparative Example 3 and Comparative Example 4, respectively. The CV test results are shown in FIG7 , where FIG7 (a), (b) and (c) are CV graphs of the batteries in Comparative Example 3, Comparative Example 4 and Application Example 1, respectively, and FIG7 (d) is a graph showing the relationship between the current response at the peak of the anode and the scan rate in logarithmic form. In FIG7 (a), (b) and (c), the horizontal axis Voltage (V vs.Li + / Li) represents the voltage (relative to the potential of lithium ions / metal lithium), and the vertical axis Current represents the current (mA); in Figure 7(d), the horizontal axis Log[scan rate (mVs -1)] represents the logarithm of the scan rate, and the ordinate Log[peak current (mA)] represents the logarithm of the peak current.

[0127] As can be seen from Figure 7, when b is 0.5, it means that the current is controlled by the diffusion process, and when b is close to 1, it means that the current is mainly controlled by the surface capacitance. The 70BP+SP composite negative electrode material in Comparative Application Example 4 is mainly based on diffusion and exhibits poor reaction kinetics. The BP@C@ZPO in Application Example 1 and the 40BP+SP composite negative electrode material in Comparative Application Example 3 are mainly based on surface capacitance and exhibit good reaction kinetics. The 40BP+SP composite negative electrode material in Comparative Application Example 3 also has good reaction kinetics because the content of conductive carbon is relatively high, which increases the conductivity of the material.

[0128] 8. Pseudocapacitance fitting test

[0129] The pseudocapacitance fitting test was performed on the batteries of Example 1, Comparative Application Example 3 and Comparative Application Example 4, and the results are shown in Figure 8, where Figures 8(a) and (b) are the pseudocapacitance fitting curve and pseudocapacitance contribution rate diagram of Comparative Application Example 3 at a scan rate of 2mV / s, respectively; Figures 8(c) and (d) are the pseudocapacitance fitting curve and pseudocapacitance contribution rate diagram of Comparative Application Example 4 at a scan rate of 2mV / s, respectively; Figures 8(e) and (f) are the pseudocapacitance fitting curve and pseudocapacitance contribution rate diagram of Application Example 1 at a scan rate of 2mV / s, respectively. In Figures 8(a), (c) and (e), the horizontal axis Potential (V vs.Li + / Li) represents the relative electrode potential relative to the Li electrode, the vertical axis Current Density (A / g) represents the current density (ampere per gram), and the horizontal axis Scan rate (mVs -1 ) represents the scan rate (millivolts per second), the vertical axis Contribution ratio represents the pseudocapacitance contribution rate, Diffusion controlled represents diffusion control, and Capacitive represents capacitance.

[0130] By fitting the pseudocapacitance of different samples, it is clear that Application Example 1 has the largest capacitance control ratio, indicating that the BP@C@ZPO composite anode material in Application Example 1 has excellent reaction kinetics. The pseudocapacitance ratio of the 70BP+SP sample at different scan rates is lower than that of 40BP+SP, indicating that 70BP+SP has the worst reaction kinetics. This is mainly because the phosphorus content of this sample is higher than that of 40BP+SP. Phosphorus itself has poor reaction kinetics and poor conductivity, resulting in poor reaction kinetics.

[0131] 9. Electrochemical performance test

[0132] (1) The electrochemical performance tests were carried out on the batteries of Example 1, Comparative Application Example 3 and Comparative Application Example 4. The electrochemical performance test results are shown in FIG9 , wherein FIG9 (a), (b) and (c) are the first charge and discharge and charge and discharge curves at different rates of the batteries of Comparative Application Example 3, Comparative Application Example 4 and Application Example 1, respectively. The curves in FIG9 (a) correspond to the charge and discharge curves at 7C / 4C / 2C / 1C / 0.5C / 0.1C / 0.2C rates from left to right, respectively. The curves in FIG9 (b) and (c) correspond to the charge and discharge curves at 7C / 4C / 2C / 1C / 0.5C / 0.2C / 0.1C rates from left to right, respectively. FIG9 (d) is the rate performance diagram of the batteries of Comparative Application Example 3, Comparative Application Example 4 and Application Example 1. FIG9 (e) is the long cycle performance diagram of the batteries of Comparative Application Example 3, Comparative Application Example 4 and Application Example 1 at a rate of 1C. Among them, the horizontal axis in Figure 9 (a), (b), and (c) is Specific capacity (mAh g -1 ) represents the specific capacity (mAh per gram), and the vertical axis Voltage (V) represents the voltage (volt); in Figure 9 (d) and (e), the horizontal axis Cycle number represents the number of cycles, and the vertical axis Specific capacity (mAh g -1 ) all represent specific capacity (milliampere-hours per gram).

[0133] As shown in Figure 9, the 70BP+SP composite anode material in Comparative Application Example 4 contains a high content of black phosphorus, resulting in an unstable sample structure and poor rate performance. Although the 70BP+SP material exhibits a high capacity during the initial cycle, this capacity is irreversible and decreases rapidly with cycling, accompanied by shedding and dissolution of the active material. The battery in Comparative Application Example 3 exhibits a lower capacity, with significant loss of active material and a lower capacity. In contrast, the battery prepared in Application Example 1 using the BP@C@ZPO composite anode material exhibits a higher capacity and better rate performance. Under 7C fast charging conditions, the BP@C@ZPO composite material exhibits a capacity retention rate of 60%, reaching 544 mAh / g (Figure 9(d)). At 1C charge and discharge, the battery prepared in Application Example 1 using the BP@C@ZPO composite anode material exhibits a capacity of 903 mAh / g, and after 500 cycles, the capacity retention rate remains as high as 81% (Figure 9(e)).

[0134] (2) The electrochemical performance of the batteries of Example 2, Comparative Application Example 1, and Comparative Application Example 2 was tested. At the same time, the electrochemical performance of the battery prepared by the control group Si@C of Comparative Example 1 (the preparation process of the battery is the same as that of Comparative Application Example 1) was tested. The test results are shown in Figure 10. Figure 10(a) is the rate performance diagram of Application Example 2; Figure 10(b) is the cycle performance diagram of Application Example 2 at 4C and 7C rates; Figure 10(c) is the long cycle performance diagram of Application Example 2 at 1C rate (the capacity is calculated based on the mass of black phosphorus); Figure 10(d) is the cycle stability performance diagram of Application Example 2, Comparative Application Example 1, and Control Group Si@C at 1C rate (the capacity is calculated based on the mass of silicon); Figure 10(e) is the cycle stability diagram of Application Example 2 and Comparative Application Example 2 at 1C rate. The horizontal axis Cycle number of Figures 10(a)-(e) represents the number of cycles, and the vertical axis on the left represents Specific capacity (mAh g -1 ) represent specific capacity (mAh / g), the vertical axis coulonbic efficiency on the right side of Figure 10(b) and (c) represents coulombic efficiency, and 10LPO in Figure 10(a) and (c) represents BP@C@LPO.

[0135] As can be seen from Figure 10, when different rate tests are carried out, at a rate of 7C, the battery of Application Example 2 still has a capacity of about 2000mAh / g, and compared with the rate of 0.1C, the capacity retention rate is as high as 66%. After 500 cycles at high rates of 4C and 7C, the capacity retention rates are 94% and 77% respectively. At a rate of 1C, the capacity retention rate is as high as 93% after 1000 cycles. However, the maximum capacity of Comparative Application Example 1 is only 580mAh / g under the cycle of 1C. It can be seen from Comparative Application Example 1 and the control group Si@C that after the addition of lithium phosphate to Comparative Application Example 1, the electrochemical performance of the material did not improve significantly. Instead, the performance deteriorated and the capacity was reduced, indicating that phosphate is not suitable for silicon negative electrode systems, and at the same time reflecting the uniqueness of phosphorus. Comparative Application Example 2 has a cycle retention rate of only 45%, showing poor cycle stability. It is shown that the black phosphorus / conductive carbon / lithium phosphate composite negative electrode material in the battery of Application Example 2 has excellent rate performance and long cycle stability, and is a high-quality negative electrode material for high-rate lithium-ion batteries.

[0136] (3) Graphite (Gr) and silicon-carbon material (Si content 13%) were used as negative electrode materials to prepare batteries as control groups. The preparation process of the batteries was the same as that of Application Example 1. The two control groups were respectively denoted as Gr and Si-C. Then, the electrochemical performance of Gr, Si-C, and Application Example 1 was tested. The electrochemical performance test results are shown in Figure 11. Figure 11 (a), (b), and (c) are the first charge and discharge curves of the control group Gr, the control group Si-C, and Application Example 1 batteries and the charge and discharge curves at different rates, respectively. , and the curves in Figures (a), (b), and (c) correspond to the charge and discharge curves at 0.1C, 0.2C, 0.5C, 1C, 2C, 4C, and 7C rates from right to left respectively; Figure 11 (d) is the rate performance diagram of the control group Gr, the control group Si-C, and the application example 1 battery; Figure 11 (e) is the long cycle performance diagram of the application example 1 at a 4C rate; Figure 11 (f) is the cycle performance diagram of the control group Gr at a 0.65C rate, the application example 1, and the control group Si / C at a 1C rate. Among them, the horizontal axis in Figures 11 (a), (b), and (c) is Specific capacity (mAh g -1 ) represents the specific capacity (mAh g), and the vertical axis Voltage (V) represents the voltage (V); in Figure 11 (d), (e), and (f), the horizontal axis Cycle number represents the number of cycles, and the vertical axis on the left represents the specific capacity (mAh g -1 ) represent the specific capacity (mAh / g), and the right vertical axis coulonbic efficiency in Figure 11(e) and (f) represents the coulombic efficiency.

[0137] As shown in Figure 11, the discharge capacity of the control Gr was 440 mAh / g at a 0.1C rate. Under 7C fast charge conditions, the discharge capacity of the control Gr was 25 mAh / g, only 6% of the 0.1C rate. This is because graphite is a layered material with an interlayer spacing of 0.335 nm. Solvated lithium ions need to undergo a desolvation step before being transported between the graphite layers. When the current is high, it is difficult for lithium ions to quickly enter the graphite for transport, resulting in ineffective lithium ion utilization, low capacity, and poor rate performance. The control Si-C had an initial discharge capacity of 800 mAh / g and an average discharge capacity of 654 mAh / g at a 0.1C rate. Under 7C fast charge conditions, the capacity was 72 mAh / g, with a retention rate of 11%. Application Example 1, charged and discharged at a current density of 0.1C, had an initial charge capacity of 1300 mAh / g, a capacity retention rate of up to 60%, and a capacity of 544 mAh / g. When charged and discharged at 1C, the capacity of Application Example 1 is 903mAh / g, and after 500 cycles, the capacity retention rate can still be as high as 81%. Even after 300 cycles at a high rate of 4C, there is still a capacity of 511mAh / g, and the retention rate is 86%. At the same time, after 500 cycles at a rate of 1C, the capacity of the control group Si-C increased from 413mAh / g to 601mAh / g, showing greater instability. The control group Gr can only be cycled at a rate of less than 1C, and has a low capacity, so it has little advantage as a fast charging material. This shows that Application Example 1 using the BP@C@ZPO composite negative electrode material has good rate performance and cycle performance, and it has great commercial potential as a negative electrode material for fast charging materials.

[0138] 10. Structural stability test

[0139] To verify the structural stability of the composite negative electrode materials of Example 1, Comparative Example 3, and Comparative Example 4, the batteries of Example 1, Comparative Application Example 3, and Comparative Application Example 4 were charged and discharged at different levels. After the procedure was completed, the batteries were disassembled, the electrode sheets were removed, cleaned with DMC, and dried in a glove box before testing. The structural stability test results are shown in Figure 12. Figure 12(a) shows the ex situ XRD contour plot of the composite negative electrode material BP@C@ZPO of Example 1 at different charge and discharge states during the first cycle, and Figure 12(b) shows the XRD patterns of the 40BP+SP / 70BP+SP / BP@C@ZPO electrode sheets of the batteries of Comparative Application Example 3, Comparative Application Example 4, and Application Example 1 after 200 cycles. The horizontal axis 2θ (degrees) of Figure 12(a) represents the diffraction angle 2θ (degrees), and the vertical axis "Status" represents the charge and discharge state; the horizontal axis 2θ (degrees) of Figure 12(b) represents the diffraction angle 2θ (degrees), and the vertical axis "Intensity" represents the diffraction intensity.

[0140] Figure 12(a) shows the formation of Li3P7 in ex situ XRD, which then disappears after charging, indicating that the black phosphorus undergoes a reversible reaction and has good structural stability. Figure 12(b) shows that the electrode of Comparative Application Example 4 exhibits a clear lithium phosphide peak after 200 cycles, indicating that the structure of the 70BP+SP material has deteriorated significantly. After 200 cycles, a small amount of LiP5 peak is also present in the 40BP+SP of Comparative Application Example 3, indicating that the material's reversibility is slightly inferior to that of BP@C@ZPO. This also demonstrates that the composite negative electrode material BP@C@ZPO of Example 1 has good structural stability.

[0141] 11. Volume expansion test

[0142] The volume expansion test was performed on the electrodes of the batteries of Use Case 1, Comparative Application Example 3, and Comparative Application Example 4 after 200 cycles. The specific process was to first cycle 2 times at a rate of 0.1C for activation, and then cycle 200 times at a rate of 1C. The batteries of Use Case 1, Comparative Application Example 3, and Comparative Application Example 4 were disassembled after 200 cycles, and the cross-sectional thickness (the thickness of the entire cross section) of the negative electrode electrodes of Use Case 1, Comparative Application Example 3, and Comparative Application Example 4 were tested using a scanning electron microscope. The SEM image is shown in Figure 13. Among them, Figures 13(a) and (b) are cross-sectional thickness test diagrams of the negative electrode sheet of Comparative Application Example 3 before and after 200 cycles; Figures 13(c) and (d) are cross-sectional thickness test diagrams of the negative electrode sheet of Comparative Application Example 4 before and after 200 cycles; Figures 13(e) and (f) are cross-sectional thickness test diagrams of the negative electrode sheet of Application Example 1 before and after 200 cycles; the scales in Figures 13(b)-(f) are the same as those in Figure 12(a).

[0143] As shown in Figure 13, the volume expansion of the negative electrode sheet of Comparative Application Example 4 was as high as 43% after 200 cycles, while the volume expansion of Comparative Application Example 3 and Application Example 1 was only 16% and 28%, respectively, showing relatively low volume expansion. The 40BP+SP composite negative electrode material of Comparative Application Example 3 contains a high proportion of amorphous conductive carbon material and has a relatively stable structure, so the volume expansion is relatively small. However, due to the porous structure of the conductive carbon material, the active material cannot be effectively exerted after black phosphorus loading, and a large amount of SEI film is easily formed, resulting in loss of active material and poor electrochemical performance. The 70BP+SP composite negative electrode material of Comparative Application Example 4 has poor structural stability, resulting in large volume expansion. The composite negative electrode material BP@C@ZPO of Application Example 1 has good structural stability and its volume expansion is relatively small.

[0144] The structural stability and reaction kinetics of the composite negative electrode materials prepared in Examples 2 and 3 of the present invention are comparable to those of the composite negative electrode material in Example 1.

[0145] In summary, the present invention adopts a specific proportion of phosphorus, conductive carbon material and phosphate composite, and the composite negative electrode material prepared by high-energy ball milling has a stable PC / PCO bond, which improves the air stability and the structural stability of the material itself; and zinc phosphate has a good adsorption effect on lithium polyphosphide, which can avoid the loss of active substances; at the same time, the amorphous composite negative electrode material can provide a better volume expansion buffer zone, slowing down the cracking and breakage of the electrode during the cycle; the phosphorus, conductive carbon material and phosphate work together to make the composite negative electrode material have excellent reaction kinetics and structural stability, thereby making the prepared battery high in capacity, good in cycle stability and rate performance, and with fast charging performance.

[0146] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A composite negative electrode material, characterized in that The invention comprises phosphorus, conductive carbon material and phosphate; the mass ratio of the phosphorus, conductive carbon material and phosphate is 4:x:y; wherein x+y=6, and x and y are both greater than 0.

2. The composite negative electrode material according to claim 1, characterized in that The phosphorus element is selected from at least one of black phosphorus and red phosphorus.

3. The composite negative electrode material according to claim 1, characterized in that The phosphate is selected from at least one of zinc phosphate, lithium phosphate and aluminum phosphate.

4. The composite negative electrode material according to claim 1, characterized in that The conductive carbon material is selected from at least one of Super P Li, acetylene black, graphite, hard carbon, soft carbon, and Ketjen black.

5. The composite negative electrode material according to any one of claims 1 to 4, characterized in that: The value of y is 0.45≤y≤5.5, and / or the value of x is 0.5≤x≤5.

55.

6. The method for preparing the composite negative electrode material according to any one of claims 1 to 5, characterized in that: The following steps are involved: The phosphorus element, the conductive carbon material and the phosphate are mixed to obtain a mixture; and the mixture is ball-milled to obtain the composite negative electrode material.

7. The preparation method according to claim 6, characterized in that The ball milling is performed using grinding balls, and the mass ratio of the grinding balls to the mixture is 45-100:

1.

8. The preparation method according to claim 6, characterized in that When the phosphorus element is black phosphorus, the method for preparing black phosphorus comprises the following steps: The black phosphorus is prepared by ball milling red phosphorus.

9. A negative electrode, characterized in that: A coating formed by the composite negative electrode material according to any one of claims 1 to 5.

10. A battery, characterized in that: The invention comprises a positive electrode, an electrolyte and the negative electrode according to claim 9.

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