Cl-doped modified LiPON solid thin film electrolyte and its preparation method

Abstract

The present invention discloses a Cl-doped modified LiPON solid thin film electrolyte and a preparation method thereof. The method uses a vacuum hot pressing sintering process and a magnetron sputtering process to prepare a LiClPON solid electrolyte thin film, replacing an appropriate amount of O sites with Cl to reduce the binding energy around P, changing the charge distribution around P in the thin film, significantly improving the ionic conductivity of the solid thin film electrolyte, and the preparation method has a simple process flow, saving high-temperature cost and time cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-solid-state thin-film lithium-ion batteries, and relates to a Cl-doped modified LiPON solid thin-film electrolyte and a preparation method thereof. Background Art

[0002] All along, the liquid lithium-ion battery industry has occupied an important position in the battery industry. The related research and technology of liquid lithium-ion batteries have gradually tended to industrial maturity, and the room for improvement of energy density has become smaller and more difficult. For the next generation of lithium-ion batteries, solid-state lithium-ion conductors are attractive electrolytes because they can effectively resist lithium dendrites, improve battery safety, and can increase the battery energy density by using a lithium metal negative electrode.

[0003] Solid electrolytes are currently divided into oxide electrolytes, sulfide electrolytes, and polymer electrolytes. Oxide electrolytes have been the most widely studied and are divided into LiSiCON, NaSiCON, perovskite type, garnet type, and amorphous LiPON type. The advantages are good chemical stability, but the room-temperature ionic conductivity is not high enough. Sulfide electrolytes have high room-temperature ionic conductivity, but poor air stability. Polymer electrolytes have high ionic conductivity, but poor mechanical properties, are sensitive to temperature, and often need to be compounded with other materials to prepare electrolytes for use.

[0004] In the technical field of all-solid-state thin-film lithium-ion batteries, LiPON has been commercialized. LiPON was first developed by the Oak Ridge National Laboratory in the United States. Magnetron sputtering of Li3PO4 targets is carried out in pure N2 or an atmosphere with a certain proportion of N2 / Ar. Its room-temperature ionic conductivity reaches 2×10 -6 S / cm, and the activation energy is Ea = 0.54 eV (Journal of Power Sources, 43-44 (1993) 103-110). It has been recognized for its wide electrochemical window and good chemical stability, but the ionic conductivity still cannot meet people's needs.

[0005] Previously, many studies have been done on LiPON thin-film electrolytes. Malachi Noked was able to prepare high-quality LiPON thin films using atomic layer deposition, but the ionic conductivity of 10 -7 S / cm is one order of magnitude lower than that of magnetron sputtering. Precursors introducing P sources and N sources need to be screened, and in practical applications, the atomic layer deposition rate is much lower than that of magnetron sputtering, and the time cost for preparing thicker solid electrolyte films is high. (Chem. Mater. 2015, 27, 5324-5331). Young Soo Yoon annealed the magnetron-sputtered amorphous LiPON thin film at 200 °C to make it partially crystalline, and successfully increased it from 1.26×10-6 The S / cm is increased to 3.31×10 -6 S / cm, and it can still maintain 91.9% of the ionic conductivity after four days. However, this method increases the cost and time cost of high-temperature sintering (Ceramics International 46(2020)14071–14077). In recent years, research has proposed the mixed cation network effect. Dongwook Shin prepared a Li3PO4·Li3BO3 composite target, and the ionic conductivity of the prepared LiBPON was only 3.52×10 -6 S / cm, and the improvement effect of the ionic conductivity is not obvious (Thin Solid Films 685(2019)434–439). Frederic Le Cras fired Li 3+x Si x P 1-x O4 single-phase crystal target, and the ionic conductivity of LiSiPON obtained by magnetron sputtering in N2 can be increased by an order of magnitude, reaching 2.2×10 -5 S / cm. However, in this method, specific-phase powder needs to be fired during the preparation process before hot pressing, and the process steps are relatively cumbersome (ACS Appl.EnergyMater.2019,2,4782-4791). Summary of the Invention

[0006] The present invention aims to provide a Cl-doped modified LiPON solid thin film electrolyte and a preparation method thereof. The method prepares a LiClPO single-phase crystal target by a simple hot pressing sintering method, and Cl is doped into LiPON by magnetron sputtering in N2 to prepare a LiClPON thin film. The process flow is simple and the ionic conductivity is significantly improved.

[0007] The technical solution of the present invention is as follows:

[0008] A Cl-doped modified LiPON solid thin film electrolyte and a preparation method thereof, comprising the following steps:

[0009] Step 1, mix and ball-mill Li3PO4 and LiCl according to the molar ratio of P to Cl of 1:x, where 1≤x≤2, to obtain a uniformly mixed powder, and load it into a graphite mold;

[0010] Step 2, place the graphite mold in a vacuum hot pressing sintering furnace, evacuate, heat up to 800-900°C at a certain heating rate, increase the pressure to 20MPa-40MPa at a certain pressure increasing rate, keep the temperature and pressure for a period of time, cool down to a certain temperature at a certain cooling rate, and decrease the pressure at a certain pressure decreasing rate, and finally cool to room temperature with the furnace to obtain a LiClPO single-phase crystal target;

[0011] Step 3: Pre-evacuate the magnetron sputtering chamber. The working gas is N2 with a flow rate of 90 sccm and a power density of 1 W / cm 2 ~1.7 W / cm 2 , and magnetron sputtering is carried out with a LiClPON single-phase crystal target to obtain a LiClPON thin film.

[0012] Preferably, in Step 1, the molar ratio of LiCl to Li3PO4 is 1:1.

[0013] Preferably, in Step 1, the rotation speed of the ball mill is 400 rpm and the ball milling time is 3 h.

[0014] Preferably, in Step 2, evacuate the vacuum hot press sintering furnace to 1×10 -5 Pa, heat it to 900 °C at a certain heating rate, increase the pressure to 32 MPa at a certain pressure increasing rate, hold the temperature and pressure for 1 h, cool it to 500 °C at a certain cooling rate, reduce the pressure to atmospheric pressure at a certain pressure reducing rate, and finally cool it to room temperature with the furnace to obtain a LiClPO single-phase crystal target.

[0015] Preferably, in Step 2, the heating rate is 10 °C / min, the pressure increasing rate is 0.7 MPa / min; the cooling rate is 1.6 °C / min, and the pressure reducing rate is 0.18 MPa / min.

[0016] Preferably, in Step 3, pre-evacuate the magnetron sputtering chamber to 1.5×10 -5 Pa, and the power density is 1.3 W / cm 2 .

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] Firstly, the process of preparing the target from the powder is simple and the composition regulation is easy; secondly, the method of room temperature magnetron sputtering is adopted, and annealing is not required after preparation, effectively reducing the time cost and high-temperature annealing cost; finally, the ionic conductivity of the solid-state thin film electrolyte is significantly improved. Description of the Drawings

[0019] Figure 1 It is the XRD pattern and physical diagram of the LiClPO single crystal target powder prepared in Examples 1 to 5.

[0020] Figure 2 It is the cross-sectional scanning electron microscope image of LiClPON prepared in Example 1.

[0021] Figure 3 It is the cross-sectional scanning electron microscope image of LiClPON prepared in Example 2.

[0022] Figure 4 It is the cross-sectional scanning electron microscope image of LiClPON prepared in Example 3.

[0023] Figure 5 It is a cross-sectional scanning electron microscope image of LiClPON prepared in Example 4.

[0024] Figure 6 It is a cross-sectional scanning electron microscope image of LiClPON prepared in Example 5.

[0025] Figure 7 It is a cross-sectional scanning electron microscope image of LiPON prepared in Comparative Example 1.

[0026] Figure 8 It is the impedance spectrogram of LiClPON prepared in Examples 1 to 5.

[0027] Figure 9 It is the impedance spectrogram of LiPON prepared in Comparative Example 1. Detailed implementation manners

[0028] The present invention will be further described in detail below in conjunction with examples and drawings, but the content of the present invention is not limited thereto.

[0029] The present invention proposes a method for doping halogen anions, which is different from the mechanisms of existing methods and has not been attempted in the previous amorphous LiPON system. The present invention dopes LiPON with halogen element Cl. First, compared with -2 valence O, -1 valence Cl has a weaker interaction with lithium ions, so it has faster lithium ion conduction ability. Secondly, the radius of halogen anions is relatively large, resulting in longer ionic bonds and greater polarizability in the compound, which is conducive to the migration of lithium ions and the improvement of plasticity. Moreover, inorganic halides with strong ionicity can remain stable in dry air or even at high temperatures.

[0030] Example 1

[0031] According to the molar ratio of P and Cl of 1:1, LiCl and Li3PO4 were weighed in a glove box under an Ar protection atmosphere and sealed in a ball milling jar. Then, the mixture was ball milled at a speed of 400 rpm for 3 h in a planetary ball mill to obtain uniformly mixed target powder. Under an Ar protection atmosphere, the powder obtained after ball milling was put into a graphite mold and sent into a vacuum hot pressing sintering furnace. The vacuum of the vacuum hot pressing sintering furnace was pumped to 1×10 -5 Pa, heated to 900 °C, the pressure was increased to 32 MPa, the heating rate was 10 °C / min, and the pressure increasing rate was 0.7 MPa; the holding time for heat preservation and pressure holding was 1 h; the cooling rate was 1.6 °C / min, and the pressure decreasing rate was 0.18 MPa / min. After cooling to 500 °C, it was cooled to room temperature with the furnace to obtain the LiClPO target. Before magnetron sputtering, the chamber needs to be pre-pumped to a vacuum of 1.5×10 -5 Pa. Under a N2 atmosphere, the flow rate was 90 sccm, and the power density was 1.1 W / cm2 LiClPON was obtained by magnetron sputtering for 20 h under certain conditions.

[0032] The electrochemical test model has a sandwich structure: ordinary glass / Cr-Ti / Pt / LiClPON / Pt, with an effective area of 25 mm 2 , and the coatings were all completed by magnetron sputtering. The tests were carried out on a Biologic electrochemical workstation, and the test frequency range was 100 KHz to 1 MHz.

[0033] Samples for morphological and compositional characterization required LiClPON to be deposited on Si substrates or ordinary glass substrates.

[0034] Example 2

[0035] According to the molar ratio of P to Cl of 1:1, LiCl and Li3PO4 were weighed in a glove box under an Ar protective atmosphere and sealed in a ball milling jar. Then, the mixture was ball milled at a speed of 400 rpm for 3 h in a planetary ball mill to obtain a uniformly mixed target powder. Under an Ar protective atmosphere, the powder obtained after ball milling was placed in a graphite mold and sent into a vacuum hot pressing sintering furnace. The vacuum in the hot pressing sintering furnace was pumped to 1×10 -5 Pa, heated to 900 °C, the pressure was increased to 32 MPa, the heating rate was 10 °C / min, and the pressure increasing rate was 0.7 MPa; the holding and pressing time was 1 h; the cooling rate was 1.6 °C / min, and the pressure decreasing rate was 0.18 MPa / min. After cooling to 500 °C, it was cooled to room temperature with the furnace, and the LiClPO target was obtained. Before magnetron sputtering, the chamber needed to be pre-pumped to a vacuum of 1.5×10 -5 Pa. Under a N2 atmosphere, the flow rate was 90 sccm, and the power density was 1.3 W / cm 2 LiClPON was obtained by magnetron sputtering for 20 h under certain conditions.

[0036] The electrochemical test model has a sandwich structure: ordinary glass / Cr-Ti / Pt / LiClPON / Pt, with an effective area of 25 mm 2 , and the coatings were all completed by magnetron sputtering. The tests were carried out on a Biologic electrochemical workstation, and the test frequency range was 100 KHz to 1 MHz.

[0037] Samples for morphological and compositional characterization required LiClPON to be deposited on Si substrates or ordinary glass substrates.

[0038] Example 3

[0039] Weigh LiCl and Li3PO4 according to the molar ratio of P to Cl of 1:1 and seal them in a ball milling jar under the protective atmosphere of Ar in a glove box. Then, ball mill them in a planetary ball mill at a rotation speed of 400 rpm for 3 h to obtain a uniformly mixed target powder. Under the protective atmosphere of Ar, put the powder obtained after ball milling into a graphite mold and send it into a vacuum hot pressing sintering furnace. The vacuum hot pressing sintering furnace is evacuated to 1×10 -5 Pa, heat it up to 900 °C, increase the pressure to 32 MPa, with a heating rate of 10 °C / min and a pressure increasing rate of 0.7 MPa; keep the temperature and pressure for 1 h; the cooling rate is 1.6 °C / min and the pressure decreasing rate is 0.18 MPa / min. After cooling to 500 °C, cool it in the furnace to room temperature to obtain the LiClPO target. Before magnetron sputtering, the chamber needs to be pre-evacuated to 1.5×10 -5 Pa. Under the atmosphere filled with N2, with a flow rate of 90 sccm and a power density of 1.5 W / cm 2 Perform magnetron sputtering for 20 h under these conditions to obtain LiClPON.

[0040] The electrochemical test model is a sandwich structure: ordinary glass / Cr-Ti / Pt / LiClPON / Pt, with an effective area of 25 mm 2 . The coatings are all completed by magnetron sputtering. Test in a Biologic electrochemical workstation, and the test frequency range is 100 KHz to 1 MHz.

[0041] For the morphological and compositional characterization of the sample, LiClPON needs to be coated on a Si substrate or an ordinary glass substrate.

[0042] Example 4

[0043] Weigh LiCl and Li3PO4 according to the molar ratio of P to Cl of 1:1.5 and seal them in a ball milling jar under the protective atmosphere of Ar in a glove box. Then, ball mill them in a planetary ball mill at a rotation speed of 400 rpm for 3 h to obtain a uniformly mixed target powder. Under the protective atmosphere of Ar, put the powder obtained after ball milling into a graphite mold and send it into a vacuum hot pressing sintering furnace. The vacuum hot pressing sintering furnace is evacuated to 1×10 -5 Pa, heat it up to 900 °C, increase the pressure to 32 MPa, with a heating rate of 10 °C / min and a pressure increasing rate of 0.7 MPa; keep the temperature and pressure for 1 h; the cooling rate is 1.6 °C / min and the pressure decreasing rate is 0.18 MPa / min. After cooling to 500 °C, cool it in the furnace to room temperature to obtain the LiClPO target. Before magnetron sputtering, the chamber needs to be pre-evacuated to 1.5×10 -5 Pa. Under the atmosphere filled with N2, with a flow rate of 90 sccm and a power density of 1.1 W / cm 2 Perform magnetron sputtering for 20 h under these conditions to obtain LiClPON.

[0044] The electrochemical test model has a sandwich structure of ordinary glass / Cr-Ti / Pt / LiClPON / Pt, with an effective area of 20 mm 2 , and the coatings are all completed by magnetron sputtering. The test is carried out on a Biologic electrochemical workstation, and the test frequency range is 100 KHz to 1 MHz.

[0045] Samples for morphological and compositional characterization need to be coated with LiClPON on a Si substrate or an ordinary glass substrate.

[0046] Example 5

[0047] According to the molar ratio of P to Cl of 1:1.5, LiCl and Li3PO4 were weighed in a glove box under an Ar protective atmosphere and sealed in a ball milling jar. Then, the mixture was ball milled at a speed of 400 rpm for 3 h in a planetary ball mill to obtain a uniformly mixed target powder. Under an Ar protective atmosphere, the powder obtained after ball milling was put into a graphite mold and sent into a vacuum hot pressing sintering furnace. The vacuum in the hot pressing sintering furnace was pumped to 1×10 -5 Pa, heated to 900 °C, pressurized to 32 MPa, with a heating rate of 10 °C / min and a pressurizing rate of 0.7 MPa; the holding and pressurizing time was 1 h; the cooling rate was 1.6 °C / min and the depressurizing rate was 0.18 MPa / min. After cooling to 500 °C, it was cooled to room temperature with the furnace to obtain the LiClPO target. Before magnetron sputtering, the chamber needs to be pre-pumped to a vacuum of 1.5×10 -5 Pa, and under a N2 atmosphere with a flow rate of 90 sccm and a power density of 1.5 W / cm 2 , magnetron sputtering was carried out for 20 h to obtain LiClPON.

[0048] The electrochemical test model has a sandwich structure of ordinary glass / Cr-Ti / Pt / LiClPON / Pt, with an effective area of 20 mm 2 , and the coatings are all completed by magnetron sputtering. The test is carried out on a Biologic electrochemical workstation, and the test frequency range is 100 KHz to 1 MHz.

[0049] Samples for morphological and compositional characterization need to be coated with LiClPON on a Si substrate or an ordinary glass substrate.

[0050] Comparative Example 1

[0051] Weigh the raw material Li3PO4 without introducing a Cl source. The powder was sent into a vacuum hot pressing sintering furnace. The vacuum in the hot pressing sintering furnace was pumped to 1×10 -5Pa, heat to 900 °C, increase the pressure to 32 MPa, with a heating rate of 10 °C / min and a pressure increase rate of 0.7 MPa; hold the temperature and pressure for 1 h; cool at a rate of 1.6 °C / min and reduce the pressure at a rate of 0.18 MPa / min. After cooling to 500 °C, cool in the furnace to room temperature to obtain the Li3PO4 target. Before magnetron sputtering, the chamber needs to be pre-evacuated to 1.5×10 -5 Pa, under a N2 atmosphere, with a flow rate of 90 sccm and a power density of 2.2 W / cm 2 Perform magnetron sputtering for 25 h under these conditions to obtain LiClPON.

[0052] The electrochemical test model is a sandwich structure: ordinary glass / Cr-Ti / Pt / LiClPON / Pt, with an effective area of 25 mm 2 , and the coatings are all completed by magnetron sputtering. Test in a Biologic electrochemical workstation, with a test frequency range of 100 KHz to 1 MHz.

[0053] For the morphological and compositional characterization of the sample, LiPON needs to be deposited on a Si substrate or an ordinary glass substrate.

[0054] As Figure 1 shown, the XRD pattern and the physical image of the LiClPO single-phase crystal target powder prepared by the preparation method of the present invention. All diffraction peaks are compared with the standard PDF#87-0039 and belong to the Li3PO4 phase, without the LiCl phase, indicating that Cl replaces the position of O in Li3PO4 during the hot pressing process of the mixed powder, and the peak shape of the X-ray diffraction peak is sharp and the peak intensity is relatively high.

[0055] Figure 2 This is the cross-sectional view of LiClPON in Example 1, with a thickness of 1.25 μm. The prepared film has good adhesion to the substrate, and the surface is relatively uniform, dense, without cracks, voids and other defects, and the film formation quality meets the expectations.

[0056] Figure 3 This is the cross-sectional view of LiClPON in Example 2, with a thickness of 1.6 μm. The prepared film has good adhesion to the substrate, and the surface is relatively uniform, dense, without cracks, voids and other defects, and the film formation quality meets the expectations.

[0057] Figure 4 This is the cross-sectional view of LiClPON in Example 3, with a thickness of 2.3 μm. The prepared film has good adhesion to the substrate, and the surface is relatively uniform, dense, without cracks, voids and other defects, and the film formation quality meets the expectations.

[0058] Figure 5Cross-sectional view of LiClPON in Example 2, with a thickness of 1.6 μm. The prepared film adheres well to the substrate, and its surface is relatively uniform, dense, without defects such as cracks and voids, and the film formation quality meets the expectations.

[0059] Figure 6 Cross-sectional view of LiClPON in Example 2, with a thickness of 1.35 μm. The prepared film adheres well to the substrate, and its surface is relatively uniform, dense, without defects such as cracks and voids, and the film formation quality meets the expectations.

[0060] Figure 7 Cross-sectional view of LiPON in Comparative Example 1, with a thickness of 2 μm. The prepared film adheres well to the substrate, and its surface is relatively uniform, dense, without defects such as cracks and voids, and the film formation quality meets the expectations.

[0061] Figure 8 AC impedance spectra of LiClPON from Example 1 to Example 5. Taking the semicircle diameter value as the impedance value of the solid-state thin-film electrolyte, the impedances are 90 Ω, 85 Ω, 195 Ω, 227 Ω, and 215 Ω respectively.

[0062] Figure 9 AC impedance spectrum of LiPON in Comparative Example 1, with an impedance of 460 Ω.

[0063] Table 1 shows the parameters of Example 1 to Example 5 and Comparative Example 1. The ionic conductivity is calculated according to the formula σ = d / (R·A), where d is the thickness of the solid-state electrolyte film, R is the impedance value measured by the AC impedance spectrum, and A is the effective area for lithium-ion transport. It can be found that the ionic conductivity of Example 1 to Example 5 has a significant improvement compared with Comparative Example 1. This is because in the prepared LiClPON film, the position of O in the dispersed Li3PO4 tetrahedral structure is replaced by an appropriate amount of Cl, which reduces the binding energy of P and changes the charge distribution around P in the film, increasing the number of mobile lithium ions, thus improving the ionic conductivity of the film.

[0064] Table 1

[0065]

Claims

1. A preparation method of Cl-doped modified LiPON solid thin film electrolyte, characterized in that, It includes the following steps: Step 1: Mix and ball-mill Li3PO4 and LiCl at a molar ratio of P to Cl of 1:x, where 1 ≤ x ≤ 2, to obtain a uniformly mixed powder. Step 2: Put the above powder into a vacuum hot-pressing sintering furnace, evacuate the air, heat it to 800 - 900 °C at a certain heating rate, increase the pressure to 20 MPa - 40 MPa at a certain pressure-increasing rate, hold the temperature and pressure for a period of time, cool it to a certain temperature at a certain cooling rate, reduce the pressure at a certain pressure-reducing rate, and finally cool it to room temperature with the furnace to obtain a single-phase LiClPO crystal target. Step 3, the magnetron sputtering chamber is pre-evacuated, the working gas is N2, the flow rate is 90 sccm, and the power density is 1 W / cm 2 ~1.7W / cm 2 , and LiClPON thin film is obtained by magnetron sputtering using LiClPON single-phase crystal target.

2. The method according to claim 1, wherein The molar ratio of LiCl to Li3PO4 is 1:

1.

3. The method according to claim 1, wherein In Step 1, the rotation speed of the ball mill is 400 rpm and the ball-milling time is 3 h.

4. The method according to claim 1, characterized in that, In Step 2, the vacuum hot pressing sintering furnace is evacuated to 1×10 -5 Pa, heated to 900 °C at a certain heating rate, pressurized to 32 MPa at a certain pressure increasing rate, kept at temperature and pressure for 1 h, cooled to 500 °C at a certain cooling rate, depressurized to atmospheric pressure at a certain pressure decreasing rate, and finally cooled to room temperature with the furnace to obtain a single-phase LiClPO crystal target.

5. The method according to claim 1, characterized in that, In Step 2, the heating rate is 10 °C / min, the pressure-increasing rate is 0.7 MPa / min; the cooling rate is 1.6 °C / min, and the pressure-reducing rate is 0.18 MPa / min.

6. The method according to claim 1, wherein In Step 3, during magnetron sputtering, the flow rate is 90 sccm and the power density is 1 W / cm 2 ~1.7 W / cm 2 .

7. The method according to claim 1, wherein In Step 3, the magnetron sputtering chamber is pre-evacuated to 1.5×10 -5 Pa, and the power density is 1.3 W / cm 2 .

8. A Cl-doped modified LiPON solid thin film electrolyte prepared by the method according to any one of claims 1 - 7.

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