CN114361459B

CN114361459B - Preparation method of silver phosphide-carbon material composite and solid lithium ion battery comprising same

Info

Publication number: CN114361459B
Application number: CN202210260902.3A
Authority: CN
Inventors: 蒋茹; 齐浩军; 彭祖铃
Original assignee: China Lithium Battery Technology Co Ltd
Current assignee: China Lithium Battery Technology Co Ltd
Priority date: 2022-03-17
Filing date: 2022-03-17
Publication date: 2022-06-07
Anticipated expiration: 2042-03-17
Also published as: CN114361459A

Abstract

A solid state lithium ion battery comprising a silver phosphide-carbon material composite and a method of making the composite are disclosed. The solid lithium ion battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the active material layer of the negative electrode contains Ag_xP-C, the electrolyte is a sulfide solid electrolyte. The preparation method comprises (1) mixing silver powder and a carbon material according to the mass ratio of 0.5: 1-20: 1 to obtain a silver/carbon mixture; (2) and (3) in a tubular furnace, according to the mass ratio of a phosphating agent to the silver/carbon mixture of 0.5: 1-15: 1, placing the phosphating agent in a second porcelain boat at an upper air inlet, placing the silver/carbon mixture in a first porcelain boat at a lower air inlet, reacting and cooling to obtain the silver phosphide-carbon material composite. By containing the composite, Li is formed at the interface of the negative electrode and the solid electrolyte₃P, improves the ionic conductivity of the interface, and the carbon particles are Li₃The volume change of the P generated in the lithium insertion-extraction process provides a containing space, so that a more stable negative electrode is obtained, and the lift cycle performance, the rate capability and the service life of the battery can be improved.

Description

Preparation method of silver phosphide-carbon material composite and solid lithium ion battery comprising same

Technical Field

The invention relates to the field of lithium batteries, in particular to a method for preparing silver phosphide-carbon material composite Ag_xP-C (x = 1-15 in the formula), and a solid-state lithium ion battery in which the negative electrode active material layer contains the silver phosphide-carbon material composite and the electrolyte is sulfide solid electrolyte.

Background

The traditional lithium ion battery adopts liquid electrolyte containing flammable organic solvent, and has potential safety hazards such as heating, explosion and the like. The development of all-solid-state lithium ion batteries is one of the feasible technical approaches for improving the safety of the batteries. In the all-solid-state lithium ion battery, the electrode and the solid electrolyte are in solid-solid phase contact, and compared with the solid-liquid phase contact between the electrode and the liquid electrolyte, the interface contact resistance is higher, and meanwhile, the cycle performance and the rate performance of the all-solid-state lithium ion battery are also obviously influenced by the interface compatibility and the stability. Thus, the interface problem becomes the key to determine the electrochemical performance of the all-solid-state lithium ion battery.

Sulfide solid electrolyte is mostly adopted in the solid lithium ion battery,interfacial side reactions occur when the sulfide solid electrolyte is in contact with a metallic lithium negative electrode, e.g. LPSX + Li → Li₂S + Li₃P + LiX, the reaction product forms a solid electrolyte interface phase (SEI) which is unstable in thermodynamics and low in ion conductivity, so that interface impedance is increased, uneven space charge distribution is caused, dendritic crystal growth is induced, and the stability of the interface of the sulfide electrolyte and the metal lithium cathode is reduced, so that the attenuation and the failure of the battery capacity are accelerated.

In recent years, studies have found that Li having high ionic conductivity and electron insulating properties₃P is expected to improve the lithium ion migration rate as an interface layer material. For example, patent CN 110518254 a discloses a negative electrode current collector for lithium battery having a metal phosphide layer obtained by performing a modification treatment on the surface of a conductive current collector by using phosphorus gas. However, lithium is intercalated and deintercalated into and from Li during charge and discharge cycles₃P, repeated fracture and regeneration of the solid electrolyte interphase, will produce a large volume change and eventually deplete the electrolyte.

Therefore, there is still a need for further improvement of the negative active material of the solid-state lithium ion battery to solve the above-mentioned interface problem between the negative active material and the solid electrolyte, and to improve the interfacial ionic conductivity and interfacial stability, thereby improving the capacity, cycle performance and service life of the all-solid-state lithium ion battery.

Disclosure of Invention

In order to solve the above problems of the prior art, the present inventors have found through extensive experiments that a silver phosphide-carbon material composite Ag is obtained by treating a mixture of silver powder and a carbon material by a porcelain boat low-temperature phosphating method_xP — C, using the composite as a negative electrode active material, while using a sulfide solid electrolyte as an electrolyte, can solve the above-mentioned problems of the prior art.

Accordingly, in one aspect, the present invention provides a solid-state lithium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein an active material layer of the negative electrode contains a silver phosphide-carbon material composite Ag_xP-C (x = 1-15 in the formula), wherein the electrolyte is a sulfide solid electrolyte.

In another aspect, the present invention provides a method for preparing silver phosphide-carbon material complex Ag_xA method of P-C (wherein x = 1-15) comprising the steps of:

(1) mixing silver powder and a carbon material according to the mass ratio of 0.5: 1-20: 1 to obtain a silver/carbon mixture;

(2) and (2) in a tubular furnace into which protective gas is introduced, placing a phosphating agent in a second porcelain boat positioned at an upper air inlet according to the mass ratio of the phosphating agent to the silver/carbon mixture of 0.5: 1-15: 1, placing the silver/carbon mixture in a first porcelain boat positioned at a lower air inlet, heating the tubular furnace for reaction, and cooling to room temperature after the reaction is completed to obtain the silver phosphide-carbon material composite.

When the solid lithium ion battery of the present invention is charged, lithium ions migrate to the negative side to be reduced into lithium atoms and to be reacted with Ag_xP contact reacts to produce Li with high ionic conductivity₃P and lithium silver solid solution, and the existence of carbon and metallic silver improves the electronic conductivity of the negative electrode side and promotes

Promote solid phase diffusion. The increase of the products of high ionic conductivity at the interface is beneficial to the rapid migration of lithium ions. The phosphorus element is beneficial to the dispersion of silver, the uniformly dispersed silver is used as an active site to induce the uniform deposition of lithium, and the problem of dendritic crystal growth caused by the non-uniform deposition of lithium is avoided. The reduction potential of the lithium silver solid solution is higher than that of the lithium metal negative electrode (0.2V), so that the lithium silver solid solution is in contact with the sulfide solid electrolyte to relieve the interface reaction and reduce the interface impedance. Moreover, due to Li₃P has electrical insulation property and can be reversibly converted

Proceed slowly, but the presence of metallic silver in combination with carbon promotes Li₃The electron conductivity of P accelerates the solid phase diffusion rate. Further, the voids generated due to stacking of small-sized carbon having a certain mechanical strength in the composite are Li₃The volume change of the P provides an accommodation space, so that the direct contact between a deposited lithium metal layer and a solid electrolyte is avoided, the interface reaction is slowed down, and the cathode is more stable.

Therefore, according to the solid-state lithium ion battery provided by the invention, the interfacial ionic conductivity and the interfacial stability between the negative electrode active material layer and the solid electrolyte are greatly improved, so that the solid-state lithium ion battery has higher capacity, better cycle performance and longer service life.

Drawings

The present invention will be described in more detail and with reference to the following detailed description, taken in conjunction with the accompanying drawings, wherein:

fig. 1 is an SEM (scanning electron microscope) image of the surface of a negative electrode according to example 1 of the present application;

fig. 2 is an SEM image of the surface of the anode according to example 2 of the present application;

fig. 3 is an SEM image of the surface of the anode according to example 3 of the present application;

fig. 4 is an SEM image of the surface of the anode according to example 4 of the present application;

fig. 5 is an SEM image of the surface of the anode according to comparative example 1 of the present application;

fig. 6 is an SEM image of the surface of the negative electrode according to comparative example 2 of the present application;

fig. 7 is an SEM image of the surface of the anode according to comparative example 3 of the present application;

fig. 8 is an SEM image of the surface of the anode according to comparative example 4 of the present application; and

FIG. 9 is a graph of specific capacity versus cycle number for batteries according to examples 1-4 of the present application and comparative examples 1-4.

Detailed Description

In the following detailed description, technical features related to different embodiments of the present application may be combined with each other as long as they do not conflict with each other.

In one aspect, the present invention provides a solid-state lithium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein an active material layer of the negative electrode contains a silver phosphide-carbon material composite (Ag)_xP-C, wherein x = 1-15), and the electrolyte is a sulfide solid electrolyte.

In one embodiment of the solid-state lithium ion battery according to the present invention, the mass ratio of the silver phosphide to the carbon material is 0.5:1 to 30:1, preferably 1:1 to 15:1, and more preferably 1:1 to 10: 1.

In another embodiment of the solid-state lithium ion battery according to the present invention, the carbon material is one or more selected from carbon powder, carbon nanotubes, graphene, carbon black, carbon nanowires, activated carbon.

In another embodiment of the solid state lithium ion battery according to the present invention, the sulfide solid electrolyte is selected from the group consisting of formula LiPSX (wherein X is F, Cl, Br, I) or formula Li_7-x-yPS_6-x-yCl_xBr_y(x is more than or equal to 0 and less than or equal to 2, and y is more than or equal to 0 and less than or equal to 2) as shown in the formula; li in glassy state₂S-P₂S₅(ii) a Crystalline form of Li_zM_yPS_z(wherein x +4y +5 =2z, 0. ltoreq. y.ltoreq.1, M is one or more selected from Si, Ge, Sn); li in the form of glass-ceramic₂S-P₂S₅Or Li₆PSX (X in the formula is Cl, Br, I) or a plurality of PSX.

In another embodiment of the solid state lithium ion battery according to the present invention, the active material layer of the positive electrode comprises one or more materials selected from the group consisting of: LiCoO₂，LiMn_xO₂(wherein x is 1 or 2) LiNi_1-xMn_xO₂(wherein 0)<x<1)，LiNi_1-x-yCo_xMn_yO₂(where x is 0. ltoreq. x.ltoreq.0.5, and y is 0. ltoreq. y.ltoreq.0.5), and LiFePO₄。

In another embodiment of the solid state lithium ion battery according to the present invention, the positive electrode active material layer further comprises a conductive agent and a binder.

In another embodiment of the solid state lithium ion battery according to the present invention, the conductive agent is one or more selected from the group consisting of a carbon black conductive agent including acetylene black, 350G, carbon fiber (VGCF), Carbon Nanotube (CNT) and ketjen black, a graphite conductive agent including KS-6, KS-15, SFG-6 and SFG-15, and a graphene conductive agent including single-or multi-layer graphene or a combination thereof; the binder is one or more selected from vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), Polyacrylonitrile (PAN), polymethyl methacrylate, Styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC).

In another embodiment of the solid state lithium ion battery according to the present invention, the current collector of the negative electrode is one or more selected from the group consisting of copper foil, copper foam, nickel foam, iron foam, stainless steel sheet.

In another aspect, the invention provides a method for preparing silver phosphide-carbon material composite Ag_xA method of P-C (wherein x = 1-15) comprising the steps of:

In one embodiment of the method for preparing a silver phosphide-carbon material composite according to the present invention, the mass ratio of the silver powder to the carbon powder is 2:1 to 10:1, and the mass ratio of the phosphating agent to the silver/carbon mixture is 3:1 to 10: 1.

In one embodiment of the method for producing a silver phosphide-carbon material composite according to the present invention, the particle size range of silver is D50. ltoreq.200 nm, preferably D50. ltoreq.60 nm; the particle size range of the carbon is D50 ≤ 100nm, preferably D50 ≤ 35 nm.

The smaller the particle size of silver and the particle size of carbon is, the more advantageous in view of rapidity of reaction and uniformity of reaction, because not only the reaction time can be shortened, but also the mixing of silver and carbon can be more sufficient, thereby improving the cycle performance of the battery.

In another embodiment of the method for preparing a silver phosphide-carbon material composite according to the present invention, the phosphating agent is a substance capable of generating phosphine upon reaction or heating, such as a mixture of phosphorus and a strong base, examples of which include sodium hydroxide, potassium hydroxide and the like, or a hypophosphite.

For example, the equation for the reaction of a mixture of phosphorus and a strong base to produce phosphine, the equation for the reaction of hypophosphite to decompose to produce phosphine, and the equation for the reaction of phosphine and silver are as follows:

4P+3KOH+3H₂O → PH₃↑+3KH₂PO₂

2NaH₂PO₂ → Na₂HPO₄+PH₃↑

2PH₃+6Ag → 2Ag₃P+3H₂↑

in another embodiment of the method for preparing a silver phosphide-carbon material composite according to the present invention, the hypophosphite is one or more selected from the group consisting of sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, aluminum hypophosphite, ammonium hypophosphite, nickel hypophosphite and cobalt hypophosphite.

In another embodiment of the method for producing a silver phosphide-carbon material composite according to the present invention, the heating in step (2) is performed in the following manner: firstly, preserving the heat for 30min at 20 ℃; then, heating to 350-650 ℃, preferably 350-550 ℃, more preferably 400-550 ℃ at a rate of 1-15 ℃/min, preferably 2-10 ℃/min, more preferably 2-5 ℃/min; and then preserving the heat for 0.1-24 hours, preferably 1-8 hours, and more preferably 1-4 hours.

In the invention, metal phosphide containing silver element and phosphorus element is prepared by low-temperature phosphorization, and carbon is further mixed, thereby obtaining the silver phosphide/carbon composite anode material. The metal silver can improve the electrical insulation performance of the phosphorus, the silver phosphide can be dispersed due to the existence of the carbon, the effects of relieving volume expansion and preventing electrochemical agglomeration are achieved, the agglomeration and the volume expansion of silver particles can be effectively relieved by the carbon, the stability of the negative electrode is further improved, and the silver, the phosphorus and the carbon act synergistically, so that the purposes of improving the ionic conductivity and the stability of the interface are achieved.

In the present invention, when the composite anode material of the present invention is applied to a solid-state lithium ion battery, Li is present during discharge⁺Passes through the electrolyte to the negative electrode side to be reduced into lithium atoms, and is phosphatedSilver Ag_xP is, for example, Ag₃P reacts to generate Li with high ionic conductivity₃P and metallic silver, the reaction equation is as follows:

Ag₃P﹢3Li → Li₃P﹢3Ag

Ag﹢xLi → Li_xAg

product Li₃P has high ionic conductivity, so that an interface layer having high ionic conductivity is constructed and formed between the sulfide solid electrolyte and the negative electrode. In addition, due to Li₃P has electrical insulation property and can be reversibly converted

Slow progress due to the presence of metallic silver in combination with carbon to promote Li₃The electron conductivity of P accelerates the solid phase diffusion rate. Furthermore, the composite cathode material has a certain mechanical strength, and the gap generated by stacking small-size carbon is Li₃The volume change of the P provides an accommodation space, prevents the deposited lithium metal layer from directly contacting with the solid electrolyte, slows down the interface reaction and enables the cathode to be more stable.

The silver phosphide in the silver phosphide/carbon composite according to the present invention forms Li having high ionic conductivity in situ at the interface of the negative electrode and the solid-state electrolyte₃The P protective layer is beneficial to the rapid migration of lithium ions; the small-size carbon particles in the composite negative electrode material are Li₃The accommodating space is provided by the huge volume change of P generated in the processes of lithium intercalation and lithium deintercalation, so that a more stable cathode is obtained, and the cycling stability of the battery is improved; lithium ions migrate to the negative electrode side in the discharging process and are reduced into lithium atoms, and the lithium atoms are contacted with metal phosphide in the composite negative electrode material to react to generate Li with high ionic conductivity₃P and lithium silver solid solution, the electron conductivity of the negative electrode side is improved by utilizing carbon and metallic silver, and the method is favorable for

Reversible transformation promotes interface solid phase diffusion; the phosphorus element is beneficial to the dispersion of silver, the uniformly dispersed silver is used as an active site to induce the uniform deposition of lithium,the problem of dendritic crystal growth caused by uneven deposition of lithium is avoided; the reduction potential of the lithium silver solid solution is higher than that of the lithium metal cathode, so that the lithium silver solid solution is in contact with the sulfide solid electrolyte to relieve the interface reaction, and the interface impedance is reduced.

According to the embodiment of the invention, in the preparation process of the negative electrode, the mass ratio of the silver phosphide/carbon composite, the conductive agent and the binder can be 7:2: 1-9: 0: 1.

In order that the invention may be more fully understood, the following examples are set forth. These examples are intended to illustrate embodiments of the invention and should not be construed as limiting the scope of the invention in any way.

The following examples are illustrative, and the specific reactants and reaction conditions for a particular compound may be modified, as recognized by one skilled in the art. The starting materials for the following schemes are either commercially available or can be readily prepared from commercially available starting materials by those skilled in the art.

Example 1

< preparation of silver phosphide/carbon composite >

Weighing 2.0g of silver powder and carbon black according to the mass ratio of 1:1, stirring for 5min by using a stainless steel rod to obtain a silver-carbon mixture, and placing the silver-carbon mixture into a porcelain boat. 0.83g of red phosphorus and 0.625g of solid potassium hydroxide were weighed out in a ratio of silver-carbon mixture to red phosphorus of 1.67:1 and placed in another porcelain boat. Two ceramic boats are placed in a tube furnace, the latter is arranged at an upper air inlet, and the former is arranged at a lower air inlet. Introducing argon gas into the tubular furnace as protective atmosphere, heating the tubular furnace to 350 ℃ at the speed of 2 ℃/min, preserving the heat for 4 hours at the temperature, and then carrying out programmed cooling to room temperature to obtain the silver phosphide/carbon composite Ag_1.2P-C, the chemical formula of the silver phosphide is Ag through energy spectrum analysis_1.2P。

< preparation of negative electrode >

The silver phosphide/carbon composite prepared as above, ketjen black and PVDF were mixed in a mass ratio of 8:1:1, the mixture was put into a dry mortar and ground at a constant speed for 10min, and then 100 μ l of N-methylpyrrolidone was added and mixed to prepare a uniform slurry. Coating the slurry on a copper foil to form a coating with the thickness of 100 mu m, then placing the coating in a vacuum oven, standing the coating for 12 hours at the temperature of 100 ℃, taking out the coating, and stamping the coating into a negative plate.

< preparation of Positive electrode >

NCM811, acetylene black and PVDF were mixed in a mass ratio of 7:2:1, and 120. mu.l of N-methylpyrrolidone was added and mixed to prepare a uniform slurry. And uniformly coating the slurry on an aluminum foil, then placing the aluminum foil in a vacuum oven, standing the aluminum foil at 100 ℃ for 12 hours, taking out the aluminum foil, and stamping the aluminum foil into a positive plate.

< preparation of Battery >

0.2g of LPSCl electrolyte was weighed into a dry glove box and pressed into a dense electrolyte sheet with a thickness of 1 mm. The 2032 type button cell is assembled by a negative pole button, a negative pole piece, electrolyte, a positive pole piece, foam nickel, a stainless steel gasket and a positive pole button in sequence.

< test items and results >

Through measurement, the charge-discharge cutoff voltage is 2.7-4.2V, the current density is 0.2C, the first charge-discharge capacity is 188.05 mAh/g, the first charge-discharge efficiency is 83.96%, and the capacity retention rate is 86% after 100 cycles. FIG. 1 shows the negative electrode of this example deposited at 1 mAh.cm via a symmetrical cell^-2SEM image of the surface after lithium metal. It can be seen that the surface of the negative electrode is flat and free of dendrites and cracks.

Example 2

Weighing 4g of silver powder and 4g of graphene according to the mass ratio of 3:1, stirring for 5min by using a stainless steel rod to obtain a silver-carbon mixture, and placing the silver-carbon mixture on the plane of a porcelain boat. 0.30g of red phosphorus and 0.225g of solid potassium hydroxide were weighed out in a mass ratio of silver-carbon mixture to red phosphorus of 13.3:1 and placed on the surface of another porcelain boat. And simultaneously placing the two porcelain boats into a tube furnace, placing the porcelain boat filled with the ammonium hydrogen phosphate at an upper air inlet, and placing the porcelain boat filled with the silver-carbon mixture at a lower air inlet. Introducing argon gas into the tubular furnace to ensure that the temperature of the tubular furnace is raised to 650 ℃ at the speed of 5 ℃/min, preserving the heat for 2 hours at the temperature, and then carrying out programmed cooling to room temperature to obtain the silver phosphide/carbon composite Ag₁₀P-C. The chemical formula of the silver phosphide is Ag determined by energy spectrum analysis₁₀P。

Subsequently, a negative electrode sheet was prepared as follows. The composite negative electrode material, the acetylene black and the CMC are mixed according to the mass ratio of 7:2:1, the weighed mixture is placed in a clean and dry mortar for uniform grinding for 10min, then 100 microliter of N-methyl pyrrolidone is added, and the mixture is mixed into viscous uniform slurry without particles. The slurry was coated on a copper foil wiped and dried with absolute ethanol to a coating thickness of 100 μm. And (3) placing the copper foil coated with the slurry in a vacuum oven, standing at 100 ℃ for 12h, taking out, and stamping to obtain the negative plate. And transferring the punched negative plate into a glove box filled with argon protective atmosphere.

< preparation of Positive electrode >

< preparation of Battery >

< test items and results >

The charge-discharge cut-off voltage is 2.7-4.2V, the current density is 0.2C, the first charge-discharge capacity is 171.88 mAh/g, the first charge-discharge efficiency is 80.09%, and the capacity retention rate is 88% after 100 cycles. FIG. 2 shows the negative electrode of this example deposited at 1 mAh.cm via a symmetrical cell^-2SEM image of the surface after lithium metal. It can be seen that the surface of the negative electrode was flat and free of dendrites and cracks.

Example 3

Weighing 4g of silver powder and hollow carbon nanospheres according to the mass ratio of 3:1, stirring for 5min by using a stainless steel rod to obtain a silver-carbon mixture, and placing the silver-carbon mixture on the plane of a porcelain boat. 3g of calcium hypophosphite is weighed according to the mass ratio of the silver-carbon mixture to the calcium hypophosphite of 4.8:1 and placed on the plane of another porcelain boat. Placing two ceramic boats into a tube furnace, placing the ceramic boat containing calcium hypophosphite at the upper wind gap, and filling silverThe ceramic boat of the carbon mixture is arranged at the lower air inlet. Introducing argon gas into the tubular furnace to protect the atmosphere, heating the tubular furnace to 650 ℃ at the speed of 5 ℃/min, preserving the heat for 2h at the temperature, and then cooling the temperature to room temperature by program to obtain the silver phosphide/carbon composite Ag₁₀P-C. The chemical formula of the silver phosphide is Ag determined by energy spectrum analysis₁₀P。

Subsequently, a negative electrode sheet was prepared as follows. The composite negative electrode material, CNF and PVDF prepared in the invention are mixed according to the mass ratio of 9:0:1, the weighed mixture is placed in a clean and dry mortar for uniform grinding for 10min, then 100 microliter N-methyl pyrrolidone is added, and the mixture is mixed into viscous uniform slurry without particles. The slurry was coated on a copper foil wiped and dried with absolute ethanol to a coating thickness of 100 μm. And (3) placing the copper foil coated with the slurry in a vacuum oven, standing at 100 ℃ for 12h, taking out, and stamping to obtain the negative plate. And transferring the punched negative plate into a glove box filled with argon protective atmosphere.

< preparation of Positive electrode >

NCM811, acetylene black and PVDF were mixed in a mass ratio of 7:2:1, and 120. mu.l of N-methylpyrrolidone was added and mixed to prepare a uniform slurry. And uniformly coating the slurry on an aluminum foil, then placing the aluminum foil in a vacuum oven, standing the aluminum foil for 12 hours at the temperature of 100 ℃, taking out the aluminum foil, and stamping the aluminum foil into a positive plate.

< preparation of Battery >

0.2g of LPSCl electrolyte was weighed into a dry glove box and pressed into a dense electrolyte sheet with a thickness of 1 mm. The 2032 type button cell is assembled by a negative pole button, a negative pole piece, an electrolyte, a positive pole piece, foam nickel, a stainless steel gasket and a positive pole button in sequence.

< test items and results >

The charge-discharge cut-off voltage is 2.7-4.2V, the current density is 0.2C, the first charge-discharge capacity is 169.37 mAh/g, the first charge-discharge efficiency is 78.87%, and the capacity retention rate is 79% after 100 cycles. FIG. 3 shows the negative electrode of this example deposited at 1 mAh.cm by a symmetrical cell^-2SEM image of the surface after lithium metal. It can be seen that the surface of the negative electrode was flat and free of dendrites and cracks.

Example 4

Weighing 4g of silver powder and carbon nano tubes according to the mass ratio of 3:1, stirring for 5min by using a stainless steel rod to obtain a silver-carbon mixture, and placing the silver-carbon mixture on the plane of a porcelain boat. 2.86g of sodium hypophosphite is weighed according to the mass ratio of the silver-carbon mixture to the sodium hypophosphite of 6.07:1 and placed on the plane of another porcelain boat. The two ceramic boats are simultaneously placed in a tube furnace, the ceramic boat containing sodium hypophosphite is placed at an upper air inlet, and the ceramic boat containing the silver-carbon mixture is placed at a lower air inlet. Introducing argon gas into the tubular furnace to protect the atmosphere, heating the tubular furnace to 550 ℃ at the speed of 2 ℃/min, preserving the heat for 1h at the temperature, and then cooling the temperature to room temperature by a program to obtain the silver phosphide/carbon composite Ag_14.2P-C. The chemical formula of the silver phosphide is Ag determined by energy spectrum analysis_14.2P。

Subsequently, a negative electrode sheet was prepared as follows. The composite negative electrode material, the acetylene black and the PVDF prepared in the above manner are mixed according to the mass ratio of 8:1:1, the weighed mixture is placed in a clean and dry mortar for uniform grinding for 10min, then 100 microliters of N-methyl pyrrolidone is added, and the mixture is mixed into viscous uniform slurry without particles. The slurry was coated on a copper foil wiped and dried with absolute ethanol to a coating thickness of 100 μm. And (3) placing the copper foil coated with the slurry in a vacuum oven, standing at 100 ℃ for 12h, taking out, and stamping to obtain the negative plate. And transferring the punched negative plate into a glove box filled with argon protective atmosphere.

< preparation of Positive electrode >

< preparation of Battery >

< test items and results >

The cut-off voltage of charge and discharge is 2.7-4.2V, and electricityThe current density is 0.2C, the first charge-discharge capacity is 166.17 mAh/g, the first charge-discharge efficiency is 79.62%, and the capacity retention rate is 80% after 100 cycles. FIG. 4 shows the negative electrode of this example deposited at 1 mAh.cm via a symmetrical cell^-2SEM image of the surface after lithium metal. It can be seen that the surface of the negative electrode was flat and free of dendrites and cracks.

Comparative example 1

First, an anode material was prepared as follows. 2g of silver powder is weighed and placed on the plane of the porcelain boat. 2.86g of sodium hypophosphite is weighed according to the mass ratio of the silver powder to the sodium hypophosphite of 1.05:1 and placed on the plane of another porcelain boat. The two porcelain boats are simultaneously placed in a tube furnace, the porcelain boat filled with sodium hypophosphite powder is placed at an upper air inlet, and the porcelain boat filled with silver powder is placed at a lower air inlet. Introducing argon gas protective atmosphere into the tube furnace, keeping the temperature of the tube furnace from 20 ℃ for 30min, heating to 550 ℃ at the speed of 2 ℃/min, keeping the temperature for 1h, and then cooling to room temperature by program to obtain Ag₁₀And (3) P powder. The chemical formula of the silver phosphide is Ag determined by energy spectrum analysis₁₀P。

Followed by preparation of Ag₁₀P negative plate. Mixing the Ag prepared in the above manner according to the mass ratio of 8:1:1₁₀P, acetylene black and PVDF, placing the weighed mixture into a clean and dry mortar for grinding at a constant speed for 10min, then adding 50 mu LN-methyl pyrrolidone, and mixing to form viscous uniform slurry without particles. The slurry was coated on a copper foil wiped and dried with absolute ethanol to a coating thickness of 100 μm. And (3) placing the copper foil coated with the slurry in a vacuum oven, standing at 100 ℃ for 12h, taking out, and stamping to obtain the negative plate. And transferring the punched negative plate into a glove box filled with argon protective atmosphere.

< preparation of Positive electrode >

< preparation of Battery >

< test items and results >

The charge-discharge cut-off voltage is 2.7-4.2V, the current density is 0.2C, the first charge-discharge capacity is 161.61 mAh/g, the first charge-discharge efficiency is 76.32%, and the capacity retention rate is 71% after 70 cycles. FIG. 5 shows a negative electrode of this comparative example deposited at 1 mAh.cm by a symmetrical cell^-2SEM image of the surface after lithium metal. It was observed that the surface of the negative electrode showed large, agglomerated lithium.

Comparative example 2

A metal lithium foil is selected as a negative electrode, the thickness of the metal lithium foil is 0.5mm, and a copper foil is selected as a current collector. The solid electrolyte is sulfide solid electrolyte, and the anode is NCM 811.

< preparation of Positive electrode >

< preparation of Battery >

< test items and results >

The charge-discharge cut-off voltage is 2.7-4.2V, the current density is 0.2C, the first charge-discharge capacity is 151.44 mAh/g, the first charge-discharge efficiency is 70.32%, and the capacity retention rate is 67% after 52 cycles. FIG. 6 shows a negative electrode of this comparative example deposited at 1 mAh.cm by a symmetrical cell^-2SEM image of surface after lithium metal. It was observed that bryoid lithium and a large number of dendrites appeared on the lithium metal surface of the negative electrode.

Comparative example 3

Weighing silver powder and carbon nano according to the mass ratio of 3:1The total amount of the rice tube is 4g, the mixture is stirred by a stainless steel rod for 5min to obtain a silver-carbon mixture, and the silver-carbon mixture is placed on the plane of a porcelain boat. 0.985g of sodium hypophosphite is weighed according to the mass ratio of the silver powder to the sodium hypophosphite of 0.3:1 and placed on the plane of the other porcelain boat. And simultaneously placing the two porcelain boats into a tube furnace, placing the porcelain boat filled with the ammonium hydrogen phosphate at an upper air inlet, and placing the porcelain boat filled with the silver-carbon mixture at a lower air inlet. Introducing argon gas into the tubular furnace to ensure that the temperature of the tubular furnace is raised to 650 ℃ at the speed of 5 ℃/min, preserving the heat for 2 hours at the temperature, and then carrying out programmed cooling to room temperature to obtain the silver phosphide/carbon composite Ag_0.87P-C. The chemical formula of the silver phosphide is Ag determined by energy spectrum analysis_0.87P。

< preparation of Positive electrode >

< preparation of Battery >

< test items and results >

The cut-off voltage of charge and discharge is 2.7-4.2V, the current density is 0.2C, and the first charge and discharge capacity is 149.354mAh/g, the first charge-discharge efficiency is 86.02%, and the capacity retention rate after 47 cycles is 69%. FIG. 7 shows the negative electrode of this example deposited at 1 mAh.cm through a symmetrical cell^-2SEM image of the surface after lithium metal. It can be seen that the negative electrode structure collapsed with a significant dendritic lithium.

Comparative example 4

Weighing 4g of silver powder and hollow carbon nanospheres according to the mass ratio of 3:1, stirring for 5min by using a stainless steel rod to obtain a silver-carbon mixture, and placing the silver-carbon mixture on the plane of a porcelain boat. 0.0528g of sodium hypophosphite is weighed according to the mass ratio of the silver powder to the calcium hypophosphite of 5.68:1 and placed on the plane of another porcelain boat. And simultaneously placing the two porcelain boats into a tube furnace, placing the porcelain boat filled with the ammonium hydrogen phosphate at an upper air inlet, and placing the porcelain boat filled with the silver-carbon mixture at a lower air inlet. Introducing argon gas into the tubular furnace to ensure that the temperature of the tubular furnace is raised to 650 ℃ at the speed of 5 ℃/min, preserving the heat for 2 hours at the temperature, and then carrying out programmed cooling to room temperature to obtain the silver phosphide/carbon composite Ag_15.6P-C. The chemical formula of the silver phosphide is Ag determined by energy spectrum analysis_15.6P。

Subsequently, a negative electrode sheet was prepared as follows. The composite negative electrode material, the acetylene black and the CMC are mixed according to the mass ratio of 7:2:1, the weighed mixture is placed in a clean and dry mortar to be ground for 10min at a constant speed, then 100 microliter of N-methyl pyrrolidone is added to be mixed into thick uniform slurry without particles. The slurry was coated on a copper foil wiped and dried with absolute ethanol to a coating thickness of 100 μm. And (3) placing the copper foil coated with the slurry in a vacuum oven, standing at 100 ℃ for 12h, taking out, and stamping to obtain the negative plate. And transferring the punched negative plate into a glove box filled with argon protective atmosphere.

< preparation of Positive electrode >

< preparation of Battery >

< test items and results >

The charge-discharge cut-off voltage is 2.7-4.2V, the current density is 0.2C, the first charge-discharge capacity is 177.08mAh/g, the first charge-discharge efficiency is 83.172%, and the capacity retention rate is 67% after 80 cycles. FIG. 8 shows the negative electrode of this example deposited at 1 mAh.cm via a symmetrical cell^-2SEM image of the surface after lithium metal. It can be seen that the negative electrode had significant agglomeration and the structure was covered with residual lithium, with a large number of spiky lithium dendrites on the surface.

The test results of examples 1 to 4 and comparative examples 1 to 4 above are summarized in the following table 1.

TABLE 1

Serial number	Current density C	First circle capacity mAh/g	First turn coulomb efficiency%	Cycles cycle	Capacity retention ratio%
						Example 1	0.2	188.005	83.96	100	86
Example 2	0.2	171.88	80.09	100	88
						Example 3	0.2	169.37	78.87	100	79
Example 4	0.2	166.17	79.62	100	80
						Comparative example 1	0.2	161.61	76.32	70	71
Comparative example 2	0.2	151.44	70.32	52	67
						Comparative example 3	0.2	149.354	86.02	47	69
Comparative example 4	0.2	177.08	83.172	80	67

As can be seen from Table 1 and FIG. 9, the same magnification is obtained with Ag_xThe solid-state battery formed by the P-C negative electrode has more excellent long-cycle stability, the first-circle capacity is kept above 166mAh/g, and the capacity retention rate is above 79%. In contrast to Ag_xP-cells exhibit limited cycle life, low first-turn capacity and low coulombic efficiency. The cycle life of lithium metal batteries is the worst, with a rapid decay in capacity occurring over 52 cycles. The solid solution of silver and lithium induces the lithium to be evenly nucleated, and Li is generated on the surface of the structure₃P improves the lithium ion migration rate, and the two supplement each other to provide guarantee for the long-circulating stable negative electrode. The three-dimensional structure of the carbon well ensures the stability of the cathode, reduces the interface contact with sulfide electrolyte and contains Li₃P expands in volume during cycling, exhibiting more stable cell performance.

In addition, as previously described, 1mAh/cm was deposited²After the lithium metal is used, the surface of the negative plate shows different appearances. FIGS. 1-4 maintain a smooth and intact structure, and the uniform deposition of lithium makes the particle size larger, and the surface of the structure is free of dendrites and moss-like lithium. Ag lacking carbon in FIG. 5_xThe P cathode surface showed large, agglomerated lithium. FIG. 6 shows the surface appearance of lithium metalMoss-like lithium and a large number of dendrites. FIG. 7 is similar to FIG. 5 except that the agglomerated lithium is slightly smaller, but dendrites are present. FIG. 8 is similar to FIG. 6 except that Bryoid lithium is more evident.

The present application has been described above in connection with preferred embodiments, which, however, are exemplary only and are intended to be illustrative only. On the basis of the above, the present application can be subjected to various substitutions and modifications, and the present application is within the protection scope of the present application.

Claims

1. A solid lithium ion battery comprises a positive electrode, a negative electrode and an electrolyte, wherein an active material layer of the negative electrode contains a silver phosphide-carbon material composite Ag_xP-C, wherein x = 1-15, and the electrolyte is a sulfide solid electrolyte; the silver phosphide-carbon material composite is prepared by the following method:

2. The solid state lithium ion battery according to claim 1, wherein the mass ratio of the silver phosphide to the carbon material is 0.5:1 to 30: 1.

3. The solid-state lithium ion battery according to claim 1 or 2, wherein the carbon material is one or more selected from carbon powder, carbon nanotubes, graphene, carbon black, carbon nanowires, activated carbon.

4. The solid state lithium ion battery of claim 3 wherein the sulfide solid electrolyte is selected from the group consisting of formula LiPSX, wherein X is F, Cl, Br, I, or formula Li_7-x-yPS_6-x-yCl_xBr_yWherein x is more than or equal to 0 and less than or equal to 2,y is more than or equal to 0 and less than or equal to 2, and the sulfide solid electrolyte of the thiogenitic acid is shown; li in glassy state₂S-P₂S₅(ii) a Crystalline form of Li_zM_yPS_zWherein x +4y +5 =2z, y is more than or equal to 0 and less than or equal to 1, and M is one or more selected from Si, Ge and Sn; li in the form of glass-ceramic₂S-P₂S₅Or Li₆PSX, wherein X is one or more of Cl, Br or I.

5. The solid state lithium ion battery of claim 1, wherein the active material layer of the positive electrode comprises one or more materials selected from the group consisting of: LiCoO₂；LiMn_xO₂Wherein x is 1 or 2; LiNi_1-xMn_xO₂In the formula 0<x<1；LiNi_1-x-yCo_xMn_yO₂Wherein x is 0-0.5, and y is 0-0.5; and LiFePO₄。

6. The solid state lithium ion battery of claim 5, wherein the positive electrode active material layer further comprises a conductive agent and a binder.

7. The solid state lithium ion battery of claim 6, wherein the conductive agent is one or more selected from the group consisting of a carbon black conductive agent including acetylene black, 350G, carbon fiber (VGCF), Carbon Nanotube (CNT) and ketjen black, a graphite conductive agent including KS-6, KS-15, SFG-6 and SFG-15, and a graphene conductive agent including single-or multi-layer graphene or a combination thereof; the binder is one or more selected from vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), Polyacrylonitrile (PAN), polymethyl methacrylate, Styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC).

8. The solid state lithium ion battery of claim 1, wherein the current collector of the negative electrode is one or more selected from the group consisting of copper foil, copper foam, nickel foam, iron foam, stainless steel sheet.

9. Preparation of silver phosphide-carbon material composite Ag_xThe method for P-C, wherein x = 1-15, comprises the following steps:

10. The method according to claim 9, wherein the mass ratio of the silver powder to the carbon powder is 2:1 to 10: 1; the mass ratio of the phosphating agent to the silver/carbon mixture is 3: 1-10: 1; the grain size range of the silver is D50 is less than or equal to 200 nm; the grain diameter of the carbon is D50 not more than 100 nm.

11. A process according to claim 9 or 10, wherein the phosphating agent is a substance capable of generating phosphine upon reaction or heating.

12. The method according to claim 11, wherein the substance capable of generating phosphine after the reaction or heating is a mixture of phosphorus and a strong base or a hypophosphite salt, and the hypophosphite salt is one or more selected from the group consisting of sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, aluminum hypophosphite, ammonium hypophosphite, nickel hypophosphite and cobalt hypophosphite.

13. The method according to claim 9, wherein the heating in step (2) is performed in the following manner: firstly, preserving the heat for 30min at 20 ℃; then heating to 350-650 ℃ at the speed of 1-15 ℃/min; then, the temperature is maintained for 0.1 to 24 hours.