Monocrystal hafnium-containing halofluoride interface protection layer synthesized on surface of positive electrode in situ and preparation method thereof

Abstract

The invention discloses a single crystal hafnium-containing halofluoride interface protection layer synthesized on the surface of a positive electrode in situ and a preparation method thereof, and relates to the technical field of positive electrode protection layers. According to the single-crystal hafnium-containing halogen fluoride interface protection layer, residues on the surface of a positive electrode are utilized to form a polycrystal hafnium-containing halogen fluoride interface protection layer on the surface of the positive electrode in situ, then the polycrystal hafnium-containing halogen fluoride interface protection layer is mixed with Li2S and P2S5, sintering is carried out in an inert environment, the polycrystal hafnium-containing halogen fluoride interface protection layer is converted into a single-crystal hafnium-containing halogen fluoride interface protection film, and the chemical formula of the single-crystal hafnium-containing halogen fluoride interface protection layer is LiHfFyPxS5.4-xCl6.6-y, yt; Yt; 4, 0lt; xlt; 1. The cycle life of the solid-state battery is greatly prolonged, the capacity exertion, battery energy density, rate and cycle performance of the positive electrode material are improved, the interface resistance of the solid-state electrolyte and the electrode material is reduced, the material loss in the long-term cycle process is reduced, and the service life of the solid-state battery is prolonged. And the problem of unstable electrode-electrolyte interface in the all-solid-state secondary battery is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of positive electrode protective layers, and in particular to a hafnium-containing halofluoride interface protective layer synthesized in situ on the surface of a positive electrode and a preparation method thereof. Background Art

[0002] As an emerging battery technology, solid-state batteries are mainly based on the need to improve existing battery technologies and the exploration of new battery technologies, with a focus on solving the limitations of lithium-ion batteries, such as safety, energy density, cycle life and cost. Solid-state batteries use solid electrolytes to replace liquid electrolytes in traditional lithium-ion batteries. Because solid electrolytes are non-flammable and non-volatile, they can effectively prevent battery short circuits and thermal runaway, and have higher safety. In addition, because solid electrolytes can withstand higher voltages, lithium metal can be used as the negative electrode, which greatly increases the upper limit of the battery's energy density.

[0003] Although solid-state batteries have many potential advantages, they still face some technical challenges, such as low ionic conductivity of solid electrolytes, interface problems between electrodes and electrolytes, manufacturing processes and costs, etc. Developing solid electrolytes with higher ionic conductivity and solving interface technology problems in electrolyte applications are the key to promoting solid-state batteries from the laboratory to commercialization. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide an in-situ synthesized hafnium-containing halofluoride interface protection layer on the positive electrode surface and a preparation method thereof, which greatly increases the cycle life of the solid-state battery, improves the capacity of the positive electrode material, the battery energy density, the rate and the cycle performance, reduces the interface resistance between the solid electrolyte and the electrode material, reduces the material loss during long-term circulation, and effectively solves the problem of unstable electrode-electrolyte interface in all-solid-state secondary batteries.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: providing a single crystal hafnium halogen fluoride interface protection layer synthesized in situ on the surface of the positive electrode, the single crystal hafnium halogen fluoride interface protection layer is synthesized in situ on the surface of the positive electrode using the residue on the surface of the positive electrode, and the chemical formula of the hafnium halogen fluoride interface protection layer is LiHfF y P x S 5.4-x Cl 6.6-y , where 0 <y<4,0<x<1。

[0006] Furthermore, the residue is at least one of lithium oxide, lithium hydroxide and lithium carbonate.

[0007] Furthermore, the positive electrode is composed of LiCoO 2 、LiNiO 2 、LiMn 2O 4 、LiCo 1-y M y O 2 、LiNi 1-y M y O 2 、LiMn 2-y M y O 4 、LiNi x Co y Mn z M 1-x-y-z O 2 and LiNi x Co y Mn 1-x-y O 2 At least one of the following is prepared;

[0008] Among them, M is at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti; 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

[0009] The method for preparing the above-mentioned single-crystal hafnium-containing halofluoride interface protective layer synthesized in situ on the positive electrode surface comprises the following steps:

[0010] (1) mixing the powder for preparing the positive electrode with hafnium chloride and hafnium fluoride, and then subjecting the mixture to ball milling and high-temperature sintering to obtain an in-situ synthesized polycrystalline hafnium-containing halofluoride interface protective film on the surface of the positive electrode;

[0011] (2) The polycrystalline hafnium-containing halogen fluoride interface protective film obtained in step (1) is bonded to Li 2 S and P 2 S 5 The mixed materials are sintered and ball-milled in a nitrogen environment to transform them into a single crystal niobium halide-containing interface protective film.

[0012] Furthermore, in step (1), the weight percentage of hafnium chloride and hafnium fluoride in the powder is 0.2-3%.

[0013] Furthermore, in steps (1)-(2), ball milling is performed at 50-500 rpm for 5-20 hours.

[0014] Furthermore, in step (1), during high temperature sintering, the temperature is raised to 100-500° C. at a rate of 0.5-10° C. / min and maintained for 2-10 h in an inert atmosphere.

[0015] Furthermore, in step (2), during high temperature sintering, the temperature is raised to 450-750° C. at a rate of 0.5-10° C. / min and maintained for 2-20 hours under an inert atmosphere.

[0016] A solid-state battery comprises a positive electrode, a negative electrode and an electrolyte. The positive electrode is a positive electrode containing a single-crystal hafnium-containing halofluoride interface protection layer, the negative electrode is metallic lithium, and the electrolyte is a sulfide solid electrolyte.

[0017] The present invention has the following beneficial effects:

[0018] 1. The present invention generates in situ a single-crystal hafnium-containing halofluoride interface protective layer with the help of different residues on the surface of different positive electrode active materials. The protective layer is loaded on the surface of the positive electrode. The hafnium halofluoride has high ionic conductivity and a very high electrochemical window, which can greatly improve the interfacial charge transfer and inhibit the decomposition of the electrolyte on the interface, thereby improving the rate performance and cycle life of the solid-state battery.

[0019] 2. The present invention solves the problem of interface contact between the positive electrode material and the solid electrolyte. The membrane is calcined for the second time with the help of Li 2 S and P 2 S 5 It reacts with the chloride it contains to form a solid electrolyte similar to sulfide Li 5.4 PS 4.4 Cl 1.6 The composition of the material increases its interfacial compatibility with solid electrolytes, especially sulfide solid electrolytes, when used in solid-state batteries, greatly improving the cycle life of the battery.

[0020] 3. We assembled a solid-state battery using a high-nickel positive electrode coated with a high-voltage stable hafnium halide fluoride. Under the conditions of 25°C, 4.5V cut-off voltage, the capacity retention rate after 500 cycles at a current density of 1C was about 98%. Further increasing the cut-off voltage to 4.8V, the capacity retention rate of the battery system after 200 cycles at 25°C and a current density of 1C was about 86%, which shows that the battery system exhibits excellent cycle stability under high voltage. In addition, the battery system also exhibits excellent kinetic performance, and exhibits excellent rate performance at 0°C, 25°C and 60°C. At 0°C, the solid-state battery still has 136.5mAh g at a current density of 1C. -1 Specific capacity. DETAILED DESCRIPTION

[0021] The principles and features of the present invention are described below, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific conditions are specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0022] Example 1

[0023] A single crystal hafnium-containing halofluoride interface protective film synthesized in situ on the surface of a positive electrode, the preparation method of which comprises the following steps:

[0024] The powder for preparing the positive electrode (NCM811, i.e. LiNi 0.8 Co 0.1 Mn 0.1 O 2 , 811 represents the ratio of each element), hafnium chloride (accounting for 1% of the weight of the positive electrode), and hafnium fluoride (accounting for 1% of the weight of the positive electrode) are mixed, ball-milled at 200 rpm for 10 hours, and then heated to 200° C. at a rate of 10° C. / min and kept warm for 10 hours in an inert atmosphere to obtain a polycrystalline hafnium-containing halofluoride interface protective film precursor;

[0025] The film precursor is mixed with Li 2 S (1% of the precursor weight) and P 2 S 5 (Li 2 The mixture was mixed with 0.6% by weight of S), then ball-milled at 200 rpm for 5 h, and finally heated to 500° C. at a rate of 10° C. / min and kept for 15 h in an inert atmosphere to obtain an in-situ synthesized single crystal hafnium-containing halofluoride interface protective film on the positive electrode surface.

[0026] Example 2

[0027] A single crystal hafnium-containing halofluoride interface protective film synthesized in situ on the surface of a positive electrode, the preparation method of which comprises the following steps:

[0028] The powder for preparing the positive electrode (NCM811, i.e. LiNi 0.8 Co 0.1 Mn 0.1 O 2 , 811 represents the ratio of each element), hafnium chloride (accounting for 2% of the weight of the positive electrode) and hafnium fluoride (accounting for 1% of the weight of the positive electrode) are mixed, ball-milled at 150 rpm for 5 hours, and then heated to 220° C. at a rate of 2° C. / min and kept warm for 5 hours in an inert atmosphere to obtain a polycrystalline hafnium-containing halofluoride interface protective film precursor;

[0029] The film precursor is mixed with Li 2 S (2% of the precursor weight) and P 2 S 5 (Li 2 The mixture was mixed with 0.6% by weight of S), then ball-milled at 150 rpm for 2 h, and finally heated to 600 ° C at a rate of 2 ° C / min in an inert atmosphere for 10 h to obtain an in-situ synthesized single crystal hafnium-containing halofluoride interface protection film on the positive electrode surface.

[0030] Comparative Example 1

[0031] The difference between Comparative Example 1 and Example 1 is that the amount of hafnium chloride added is 10% of the weight of the positive electrode, and the amount of hafnium fluoride added is 5% of the weight of the positive electrode.

[0032] Comparative Example 2

[0033] The difference between Comparative Example 2 and Example 1 is that the two sintering temperatures in steps (1)-(2) are 600°C.

[0034] Comparative Example 3

[0035] The difference between Comparative Example 3 and Example 1 is that the two sintering times in steps (1)-(2) are 0.5 h.

[0036] Comparative Example 4

[0037] The difference between Comparative Example 4 and Example 1 is that the heating rates in steps (1)-(2) are 20°C / min.

[0038] Comparative Example 5

[0039] The difference between Comparative Example 5 and Example 1 is that the two ball millings in steps (1)-(2) were performed at 10 rpm for 5 h.

[0040] Comparative Example 6

[0041] The positive electrode of NCM811 without any treatment.

[0042] The products obtained in Examples 1-2 and Comparative Examples 1-6 were subjected to battery testing, and the specific process is as follows:

[0043] 1. Solid-state battery assembly: The products obtained in Examples 1-2 and Comparative Examples 1-6 were respectively used with sulfide solid electrolyte and metallic lithium in a glove box (H 2 O<0.1ppm, O 2 <0.1ppm) to assemble solid-state batteries.

[0044] 2. Solid-state battery performance test:

[0045] The electrochemical performance of the prepared lithium batteries was tested using Xinwei testing equipment. The test results are shown in Table 1.

[0046] High voltage cycle: Each assembled lithium battery is subjected to 1C charge and discharge cycle test at 25°C in different voltage ranges.

[0047] Calculate the battery capacity retention rate of each lithium battery:

[0048] Battery capacity retention rate (%) = (discharge capacity of the last cycle / discharge capacity of the first cycle) × 100%.

[0049] Table 1 Capacity retention of solid-state batteries after 500 cycles

[0050]

[0051]

[0052] As can be seen from Table 1, Example 1, Comparative Example 1 and Comparative Example 6 prove that too much hafnium chloride and hafnium fluoride are not reacted on the surface and may be a damage to the battery performance; Example 1 and Comparative Example 2 show that too high a sintering temperature will reduce the interface stability of the sample obtained by sintering, and damage the voltage tolerance; Example 1 and Comparative Example 3 show that if the sintering time is too short, no interface film may be generated, and too much hafnium chloride and hafnium fluoride may not be reacted on the surface, which is harmful to the battery performance; Example 1 and Comparative Example 5 show that the heating rate has a certain influence on the battery performance; Example 1 and Comparative Example 5 show that the grinding is sufficient. Uniform mixing is beneficial to the uniformity of the interface film, thereby improving the battery performance. In general, the single crystal hafnium halide fluoride interface protective film greatly improves the high-voltage cycle performance of lithium metal solid-state batteries and increases the energy density of the battery.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A single crystal hafnium-containing halofluoride interface protective layer synthesized in situ on the surface of a positive electrode, characterized in that: The single crystal hafnium-containing halogen fluoride interface protection layer first uses the residue on the positive electrode surface to in-situ form a polycrystalline hafnium-containing halogen fluoride interface protection layer on the positive electrode surface, and then mixes with Li2S and P2S5, and sinters in an inert environment to convert it into a single crystal hafnium-containing halogen fluoride interface protection film. The chemical formula of the single crystal hafnium-containing halogen fluoride interface protection layer is LiHfF y P x S 5.4-x Cl 6.6-y , where 0 <y<4,0<x<1。 2. The single crystal hafnium-containing halofluoride interface protective layer synthesized in situ on the positive electrode surface according to claim 1, characterized in that: The surface residue is at least one of lithium oxide, lithium hydroxide and lithium carbonate.

3. The single crystal hafnium-containing halofluoride interface protective film synthesized in situ on the positive electrode surface according to claim 1, characterized in that: The positive electrode is composed of LiCoO2, LiNiO2, LiMn2O4, LiCo 1-y M y O2、LiNi 1-y M y O2、LiMn 2-y M y O4、LiNi x Co y Mn z M 1-x-y-z O2 and LiNi x Co y Mn 1-x-y At least one of O2 is prepared; Among them, M is at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V and Ti; 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

4. The method for preparing the in-situ synthesized single crystal hafnium-containing halofluoride interface protective layer on the positive electrode surface according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) mixing the powder for preparing the positive electrode with hafnium chloride and hafnium fluoride, and then subjecting the mixture to ball milling and high-temperature sintering to obtain an in-situ synthesized polycrystalline hafnium-containing halofluoride interface protective film on the surface of the positive electrode; (2) The polycrystalline hafnium-containing halide fluoride interface protective film obtained in step (1) is mixed with Li2S and P2S5, and sintered and ball-milled in a nitrogen environment to convert it into a single crystal niobium-containing halide interface protective film.

5. The method for preparing the in-situ synthesized single crystal hafnium-containing halofluoride interface protective film on the positive electrode surface according to claim 4, characterized in that: In step (1), the weight percentage of hafnium chloride and hafnium fluoride in the powder is 0.2-3%.

6. The method for preparing the in-situ synthesized single crystal niobium halide interface protective film on the positive electrode surface according to claim 4, characterized in that: In steps (1)-(2), ball milling is performed at 50-500 rpm for 5-20 h.

7. The method for preparing the in-situ synthesized single crystal hafnium-containing halofluoride interface protective film on the positive electrode surface according to claim 4, characterized in that: In step (1), during high temperature sintering, the temperature is raised to 100-500° C. at a rate of 0.5-10° C. / min and maintained for 2-10 hours in an inert atmosphere.

8. The method for preparing the in-situ synthesized single crystal hafnium-containing halofluoride interface protective film on the positive electrode surface according to claim 4, characterized in that: In step (2), during high temperature sintering, the temperature is raised to 450-750° C. at a rate of 0.5-10° C. / min and maintained for 2-20 hours in an inert atmosphere.

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