Three-dimensional lithiumophilic MXene / Ge film current collector, and preparation method and application thereof

Abstract

The present application belongs to the field of lithium metal battery negative electrode current collector, and particularly relates to a three-dimensional lithiumophilic MXene / Ge thin film current collector and a preparation method and application thereof. Ti3C2 MXene powder is first dispersed in ethanol, and after ultrasonic treatment, centrifugal separation is performed, and the upper layer dispersion liquid is reserved; the dispersion liquid is ultrasonically dispersed again and centrifuged, and the multi-layer material is separated; the upper layer liquid is suction filtered into a film and dried to obtain a MXene thin film, and the precipitate can be repeatedly treated to obtain more thin films; in an argon atmosphere, a germanium target is covered on the MXene film through magnetron sputtering to prepare a MXene / Ge thin film. The uniform Ge nanoparticles on the surface of the MXene / Ge thin film of the present application serve as lithiumophilic nucleation sites, significantly reduce the lithium nucleation barrier, induce uniform lithium metal deposition, efficiently inhibit the generation of lithium dendrites, and effectively avoid the risk of short circuit.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium metal battery negative electrode current collector, and particularly relates to a three-dimensional lithiumophilic MXene / Ge thin film current collector and a preparation method and application thereof. BACKGROUND

[0002] In order to improve the energy density of the next generation of lithium batteries, in the past decade, researchers have mainly focused on the innovation of various materials of the battery. Among high-capacity negative electrodes, lithium metal has become a research hotspot of high-energy-density batteries due to its ultra-high theoretical specific capacity (3860 mAh g -1 ) and the lowest electrochemical potential (-3.04 V relative to the standard hydrogen electrode). The current problems of lithium metal batteries include the safety problems such as short circuit of the battery caused by the penetration of the separator by lithium dendrites, the problem of "dead lithium" caused by the fracture of lithium dendrites, and the serious consumption of electrolyte, etc., which leads to low coulombic efficiency, short cycle life and safety hazards of lithium metal batteries. The above problems can be attributed to the growth of harmful dendrites and uncontrollable lithium deposition behavior.

[0003] Therefore, the technical scheme of the present application is proposed. SUMMARY

[0004] In order to solve the problems existing in the prior art, the present application provides a three-dimensional lithiumophilic MXene / Ge thin film current collector and a preparation method and application thereof. The present application directly uses the MXene thin film as the current collector of the lithium negative electrode by taking advantage of the flexible self-supporting of the MXene thin film, i.e. without the need to use a binder and a conductive agent, and a complicated slurry coating process. For lithium metal batteries, the MXene thin film as the current collector can better maintain the complete electrode structure and realize the stable contact between the substrate and the lithiumophilic substance. At the same time, it can also increase the contact area between the electrode and the electrolyte, effectively shortening the diffusion distance of ions and electrons. Importantly, the self-supporting electrode of MXene does not need to use a binder, thereby further improving the energy density of the battery. The present application magnetron sputters a layer of ultra-fine metal germanium (Ge) on the MXene thin film, effectively improving the lithiumophilic property and mechanical stability of the MXene thin film. The performance of the MXene after magnetron sputtering of Ge is better than that of the MXene current collector without sputtering.

[0005] The present application provides a preparation method of a three-dimensional lithiumophilic MXene / Ge thin film current collector, which comprises the following steps:

[0006] (1) Disperse the few-layer Ti3C2 MXene powder in a solvent, first ultrasonically disperse, then centrifuge and separate, and take the upper dispersion liquid, i.e. the few-layer dispersion liquid;

[0007] (2) ultrasonic dispersion is performed on the few-layer dispersion liquid, then centrifugal separation is performed, and then the obtained upper liquid is sequentially filtered, dried and baked to obtain a MXene film;

[0008] (3) Ge is covered on the MXene film by magnetron sputtering in an inert atmosphere, thereby obtaining the three-dimensional lithium-philic MXene / Ge film current collector.

[0009] Preferably, in step (1), the solvent is ethanol.

[0010] Preferably, in step (1), the ultrasonic dispersion time is 1-2 h.

[0011] Preferably, in step (1), the centrifugal separation speed is 3500-4000 r / min, and the centrifugal separation time is 10-15 min.

[0012] Preferably, in step (2), the ultrasonic dispersion time is 2-2.5 h.

[0013] Preferably, in step (2), the centrifugal separation speed is 3500-4000 r / min, and the centrifugal separation time is 20-25 min.

[0014] Preferably, in step (3), the magnetron sputtering is performed by operating the magnetron sputtering equipment at 200 mA for 10 min, and fixing the germanium target to uniformly cover the surface of the MXene film.

[0015] Preferably, the working voltage of the magnetron sputtering equipment is 320-370 V, and the bias voltage is 60-80 V.

[0016] Based on the same technical concept, another scheme of the present application provides a three-dimensional lithium-philic MXene / Ge film current collector prepared by the above preparation method.

[0017] Based on the same technical concept, another scheme of the present application provides an application of the three-dimensional lithium-philic MXene / Ge film current collector in preparing a lithium metal battery.

[0018] The present application has the following beneficial effects:

[0019] The uniform Ge nanoparticles on the surface of the MXene / Ge thin film of the present application serve as lithiumophilic nucleation sites, significantly reduce the lithium nucleation barrier, induce uniform lithium deposition, efficiently inhibit lithium dendrite formation, and effectively avoid short circuit risks. The MXene / Ge three-dimensional current collector lithium metal battery with a sputtered metal germanium layer has good wide-temperature adaptability and still maintains stable performance at extreme temperatures (-15℃ to 60℃), and has low polarization voltage during the cycle process, effectively prolonging the service life of the battery. The MXene self-supporting film directly serves as the current collector, eliminating the need for binders and conductive agents in the preparation of traditional electrodes, simplifying the preparation process and improving the energy density of the battery. The three-dimensional layered network of MXene combined with Ge nanoparticles provides high electrical conductivity and mechanical strength. The thickness of the electrode can be controlled during the deposition / peeling process, and the volume expansion is effectively inhibited. When paired with a LiFePO4 positive electrode, the battery has a discharge capacity of 132.46mAh g -1 .

[0020] In addition, the prior art also has a method of loading high specific capacity metal particles (such as Sb, Bi) on the film as active electrode materials by electroplating, which focuses on improving the specific capacity and simplifying the traditional coating process; and the present application uniformly deposits germanium (Ge) nanoparticles on the surface of the MXene thin film by magnetron sputtering, which uses Ge as a lithiumophilic site and is designed for lithium metal battery current collectors, reduces the lithium nucleation barrier, induces uniform lithium deposition, significantly suppresses dendrite growth, and improves the safety and cycle life of the battery, such as achieving long-term stable cycling of a symmetric battery at -15℃ and 60℃, while simplifying the electrode structure (without binders / conductive agents). The two methods differ significantly in technical route (physical sputtering vs. chemical electroplating), functional positioning (current collector optimization vs. electrode material composite), and performance target (dendrite suppression vs. capacity improvement). BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 is the XRD pattern of the three-dimensional thin film current collector in Example 1 and Comparative Example 1.

[0023] Figure 2 is the Raman spectrum of the three-dimensional lithiumophilic MXene / Ge thin film current collector in Example 1.

[0024] Figure 3is a graph of the cycle performance data for the symmetric cell assembled with the three-dimensional thin film current collector in Example 1, Comparative Example 1 at a current density of 1 mA cm -2

[0025] Figure 4 is a graph of the cycle performance data for the symmetric cell assembled with the three-dimensional thin film current collector in Example 1, Comparative Example 1 at a current density of 2 mA cm -2

[0026] Figure 5 is a graph of the cycle performance data for the MXene / Ge thin film current collector in Example 1 at a surface capacity of 4 mAh cm -2

[0027] Figure 6 is a graph of the cycle performance data for the symmetric cell assembled with the three-dimensional thin film current collector in Example 1, Comparative Example 1 at 60°C, a current density of 1 mA cm -2 , and a surface capacity of 1 mAh cm -2

[0028] Figure 7 is a graph of the cycle performance data for the symmetric cell assembled with the three-dimensional thin film current collector in Example 1, Comparative Example 1 at -15°C, a current density of 1 mA cm -2 , and a surface capacity of 1 mAh cm -2

[0029] Figure 8 is a graph of the cycle performance data for the full cell assembled with the three-dimensional thin film current collector and LFP in Example 1, Comparative Example 1 at a 1C rate.

[0030] Figure 9 is a graph of the cycle performance data for the full cell assembled with the three-dimensional thin film current collector and LFP in Example 1, Comparative Example 1 at a 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 0.2C rate. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0032] Example 1

[0033] The present application provides a preparation method of a three-dimensional lithiumophilic MXene / Ge thin film current collector, and the preparation method comprises the following steps:

[0034] ​​​​​(1) The purchased few-layer Ti3C2 MXene powder is dispersed into an ethanol solution and ultrasonically treated for 1 h; after ultrasonic treatment, centrifugal separation is performed at 3500 r / min for 10 min, and the retained upper layer of dark green liquid after removal is the few-layer dispersion liquid.

[0035] (2) The few-layer dispersion liquid is treated using an ultrasonic machine for 120 min, and then centrifugal treatment is performed at 3500 r / min for 20 min to further separate the multi-layer material; the upper layer liquid obtained after centrifugal treatment is subjected to suction filtration into a film using a celgard 3501 filter membrane, and then the MXene film is peeled off from the filter membrane after baking by a vacuum drying box, an infrared lamp or other heat sources; meanwhile, the remaining precipitated multi-layer sample after centrifugal separation can be added with appropriate ethanol for ultrasonic treatment again, and the steps are the same as above, so that as many MXene films as possible can be obtained.

[0036] (3) The sputtering cabin is filled with high-purity argon, the working voltage and bias of the magnetic device are adjusted to appropriate values, the magnetron sputtering device (supermai CJC series) is used to work at 200 mA for 10 min, the germanium target is fixed to uniformly cover the surface of the MXene film, and the MXene / Ge sample is obtained by sputtering at a working voltage of 320 V and a bias of 80 V.

[0037] Example 2

[0038] The application provides a preparation method of a three-dimensional lithiumophilic MXene / Ge thin film current collector, and the preparation method comprises the following steps:

[0039] (1) The purchased few-layer Ti3C2 MXene powder is dispersed into an ethanol solution and ultrasonically treated for 1 h; after ultrasonic treatment, centrifugal separation is performed at 3500 r / min for 10 min, and the retained upper layer of dark green liquid after removal is the few-layer dispersion liquid.

[0040] (2) The few-layer dispersion liquid is treated using an ultrasonic machine for 120 min, and then centrifugal treatment is performed at 3500 r / min for 20 min to further separate the multi-layer material; the upper layer liquid obtained after centrifugal treatment is subjected to suction filtration into a film using a celgard 3501 filter membrane, and then the MXene film is peeled off from the filter membrane after baking by a vacuum drying box, an infrared lamp or other heat sources; meanwhile, the remaining precipitated multi-layer sample after centrifugal separation can be added with appropriate ethanol for ultrasonic treatment again, and the steps are the same as above, so that as many MXene films as possible can be obtained.

[0041] (3) Fill the sputtering cabin with high-purity argon, adjust the working voltage and bias of the magnetic equipment to appropriate values, use the magnetron sputtering equipment (supermai CJC series) to work at 200 mA for 10 min, fix the germanium target so that its surface uniformly covers the MXene film. Among them, the MXene / Ge1 sample is obtained by sputtering at a working voltage of 370 V and a bias of 60 V.

[0042] Comparative Example 1

[0043] (1) Disperse the purchased few-layer Ti3C2 MXene powder into an ethanol solution and ultrasonic for 1 h; after ultrasonic, centrifugal separation is performed at 3500 r / min for 10 min, and the upper layer of ink green liquid reserved after taking out is the few-layer dispersion liquid.

[0044] (2) The few-layer dispersion liquid is treated by ultrasonic machine for 120 min, and then the solution is centrifuged at 3500 r / min for 20 min to further separate the multi-layer material. The upper layer liquid obtained after centrifugation is filtered into a film by using a celgard3501 filter membrane, and then the MXene film is peeled off from the filter membrane after baking by a vacuum drying box, an infrared lamp and other heat sources. At the same time, the multi-layer sample remaining in the sediment after centrifugal separation can be added with appropriate amount of ethanol for further ultrasonic treatment, and the steps are the same as above, so that as many MXene film samples as possible can be obtained, which is the MXene sample.

[0045] Verification Example

[0046] (I) The current collector samples obtained from Example 1 and Comparative Example 1 are tested by X-ray diffraction (XRD), and the results are shown in Figure 1 : The characteristic peaks of the MXene film obtained from Comparative Example 1 are consistent with the known reports, while the XRD spectrum of the MXene / Ge film obtained from Example 1 appears new characteristic peaks of elemental Ge and GeO2. Among them, the sharp germanium and germanium oxide peak has strong intensity, indicating that it has good crystallinity.

[0047] (II) The current collector samples obtained from Example 1 are tested by Raman spectrum, and the results are shown in Figure 2 : The two characteristic peaks of 1329 cm -1 and 1547 cm -1 confirm the existence of conductive carbon matrix in the MXene / Ge film, and the intensity ratio of amorphous carbon to graphite carbon therein is 0.97, close to 1, indicating that the contents of the two types of carbon materials are close.

[0048] (III) The current collector samples prepared from Examples 1, 2 and Comparative Example 1 are tested for asymmetric battery performance, specifically:

[0049] (1) The film samples prepared in Example 1, 2 and Comparative Example 1 were cut into 12 mm diameter discs as current collectors. The purchased lithium sheet (diameter 15.9 mm, thickness 100 pm) was punched into 11 mm diameter discs as counter electrode, Celgard 2400 was used as separator, 70 mL electrolyte (1 M LiTFSI + DOL / DME + 1% LiNO3) was filled, and 2025 type button cells were assembled in an argon atmosphere glove box.

[0050] (2) The assembled batteries were placed on the electrochemical test channel, and cycled 5 times in the voltage range of 0-1 V at a current density of 0.2 mA cm -2 , so as to pre-deposit lithium metal on the current collector.

[0051] (3) After deposition, the asymmetric battery was subjected to constant current charge and discharge test, and the current density was 1-4 mA cm -2 .

[0052] The current collectors prepared in Example 1 and Comparative Example 1 were subjected to symmetric battery test, specifically: the two lithium anodes obtained by electrochemical deposition of asymmetric battery were assembled into symmetric battery, and subjected to constant current charge and discharge test, and the current density was 1-2 mA cm -2 .

[0053] The current collectors prepared in Example 1 and Comparative Example 1 were subjected to full battery test, specifically: the lithium anode obtained by electrochemical deposition of half battery was assembled with commercial LiFePO4 electrode sheet (diameter 12 mm, surface loading 11.85 mg cm -2 ) into 2025 button full battery, the composition and amount of electrolyte were consistent with those of asymmetric battery, and the cut-off voltage range of battery charge and discharge was 2.5-3.8 V.

[0054] The current collectors prepared in Example 1 and Comparative Example 1 were subjected to symmetric battery test at a current density of 1 mA cm -2 and 2 mA cm -2 . Figure 3 It was shown that when the current density was 1 mA cm -2 , the polarization voltage of lithium anode symmetric battery using the current collector of Example 1 was stable at about 30 mV within 1320 h, while the polarization voltage of lithium anode symmetric battery using the current collector of Comparative Example 1 gradually exceeded 100 mV, and could not be maintained stable in the repeated charge and discharge process. This may be due to the accumulation of "dead lithium" caused by the continuous fracture of SEI film. As shown in Figure 4 , when the working current density reached 2 mA cm -2At this time, the battery with Ge metal layer lithium negative electrode can be stably cycled for 800 h at a stable polarization voltage of 20 mV. The subsequent polarization voltage is slightly increased to 35 mV, and no battery short circuit or failure phenomenon occurs within 1000 h. However, the lithium negative electrode symmetrical battery with MXene film cannot achieve stable operation, and its polarization voltage suddenly decays from 280 mV to 84 mV at 80 h, indicating that the battery has a serious short circuit phenomenon, which is speculated to be caused by the lithium dendrites generated inside the battery piercing the separator. Therefore, it can be seen that the lithiumophilic layer of germanium metal plays a crucial role in maintaining the stable deposition and dissolution of metal lithium, mainly due to the initial nucleation of spherical lithium of metal germanium, which plays an important role in achieving dendrite-free electrodeposition. Based on the excellent electrochemical performance of the symmetrical battery in Example 1, the lithium deposition / stripping behavior of the current collector obtained in Example 1 under high surface capacity and large current density is further explored. As shown in FIG. 8, when the cycle capacity is 4 mAh cm Figure 5 -2 and the current density is 2 mA cm -2 , the overpotential of the symmetrical battery is low, about 30 mV, and stable within the first 530 h. After that, the voltage decays to 26 mV and is stably cycled to 1500 h. Although the MXene / Ge@Li composite electrode has the unique advantages of uniform nucleation and uniform lithium deposition / stripping, when the battery is operated simultaneously under high current density and high surface capacity, a soft short circuit of the battery occurs, but this soft short circuit is quickly recovered, and the cycle stability of the battery is maintained. Overall, the battery still has excellent cycle stability. From a practical point of view, due to the diversity of scenarios and working conditions, a wide range of working temperature is essential for secondary batteries. At 60℃, Figure 6 , it is shown that the lithium negative electrode obtained in Example 1 has excellent cycle stability under 1 mA cm -2 current density and 1 mA h cm -2 surface capacity, with a cycle life of up to 1800 h. When the battery is cycled to 630 h, the lithium negative electrode voltage of Comparative Example 1 decreases rapidly, and the lithium stripping phenomenon inside the battery decreases sharply, and the battery fails. Therefore, the lithiumophilic germanium layer of the MXene film obtained in Example 1 has the function of inducing uniform deposition of lithium metal and inhibiting lithium dendrites, and this property is not affected even at high temperature. Low temperature performance is also very important for the practical application of lithium metal batteries. The present application further evaluates the electrochemical performance of the symmetrical battery at -15℃, 1 mA cm -2 current density and 1 mA h cm -2 surface capacity. Figure 7 ​It is shown that the voltage fluctuation of Comparative Example 1 is large throughout the lithium deposition / stripping process, the cycle stability is poor, and the potential difference of lithium deposition and stripping is large. However, when the thin film of Example 1 is used as a lithium negative electrode, the voltage is stable during the deposition and stripping process, the overpotential is small, and the cycle stability of the battery is significantly improved.

[0055] The current collector prepared by Example 1 and Comparative Example 1 has a current density of 1C, Figure 8 The initial discharge capacity of the LFP full battery assembled by Example 1 is shown to be 155.11 mAh g -1 , and the initial discharge capacity of the LFP full battery assembled by Comparative Example 1 is 151.12 mAh g -1 After 100 cycles, the discharge specific capacity of the LFP full battery assembled by Example 1 is maintained at 132.46 mAh g -1 , and the capacity retention rate is 85.4%. However, the discharge specific capacity of the LFP full battery assembled by Comparative Example 1 is 122.88 mAh g -1 , and the capacity retention rate is 81.3%. The reason for the difference in capacity and life of the two full batteries may be that the morphology of lithium is loose during repeated charging and discharging of MXene@Li, and there are many side reactions between the large number of irregular protrusions on the surface of the thin film and the electrolyte, which aggravate the formation of "dead lithium".

[0056] In summary, the present application provides a preparation method of a lithium metal negative electrode current collector. First, disperse Ti3C2 MXene powder in ethanol, centrifuge after ultrasonic, and reserve the upper layer dispersion liquid; ultrasonic dispersion liquid again and centrifuge, separate multi-layer material, and filter the upper liquid into a film and dry to obtain MXene film, and the precipitate can be repeatedly treated to obtain more films; in an argon atmosphere, a germanium target is covered on the MXene film by magnetron sputtering to prepare a MXene / Ge thin film. The lithium metal negative electrode current collector prepared has excellent electrochemical performance, which is due to the low nucleation overpotential and good electronic conductivity of the metal germanium layer, which can significantly reduce the nucleation barrier and realize regular and uniform lithium deposition. In view of the uniform deposition of lithium, the electrochemical performance of the lithium metal battery of the MXene / Ge three-dimensional current collector with a sputtered metal germanium layer is significantly improved. Whether at low temperature or at high temperature, the MXene / Ge negative electrode has excellent cycle stability. At the same time, when it is matched with a LiFePO4 positive electrode, the discharge capacity of the battery after 100 weeks of stable cycle at 1C reaches 132.46 mAh g -1 .

[0057] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a three-dimensional lithium-loving MXene / Ge thin film current collector, characterized in that, The preparation method includes the following steps: (1) Disperse the few-layer Ti3C2 MXene powder in a solvent, first disperse it by ultrasonication, then separate it by centrifugation, and take the upper dispersion liquid, which is the few-layer dispersion liquid; (2) The few-layer dispersion is ultrasonically dispersed, then centrifuged, and the resulting upper liquid is filtered, dried and baked in sequence to obtain an MXene film; (3) In an inert atmosphere, Ge is coated onto an MXene film by magnetron sputtering to obtain the three-dimensional lithium-loving MXene / Ge film current collector.

2. The method for preparing the three-dimensional lithium-loving MXene / Ge thin film current collector according to claim 1, characterized in that, In step (1), the solvent is ethanol.

3. The method for preparing the three-dimensional lithium-loving MXene / Ge thin film current collector according to claim 1, characterized in that, In step (1), the ultrasonic dispersion time is 1 to 2 hours.

4. The method for preparing the three-dimensional lithium-loving MXene / Ge thin film current collector according to claim 1, characterized in that, In step (1), the centrifugation speed is 3500-4000 r / min and the centrifugation time is 10-15 min.

5. The method for preparing the three-dimensional lithium-loving MXene / Ge thin film current collector according to claim 1, characterized in that, In step (2), the ultrasonic dispersion time is 2 to 2.5 hours.

6. The method for preparing the three-dimensional lithium-loving MXene / Ge thin film current collector according to claim 1, characterized in that, In step (2), the centrifugation speed is 3500-4000 r / min and the centrifugation time is 20-25 min.

7. The method for preparing the three-dimensional lithium-loving MXene / Ge thin film current collector according to claim 1, characterized in that, In step (3), the magnetron sputtering method is as follows: the magnetron sputtering equipment is operated at 200mA for 10 minutes, the germanium target is fixed, and its surface is uniformly covered on the MXene film.

8. The method for preparing the three-dimensional lithium-loving MXene / Ge thin film current collector according to claim 7, characterized in that, The operating voltage of the magnetron sputtering equipment is 320-370V, and the bias voltage is 60V-80V.

9. The three-dimensional lithium-loving MXene / Ge thin film current collector obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the three-dimensional lithium-loving MXene / Ge thin film current collector as described in claim 9 in the preparation of lithium metal batteries.

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