Solid ion conductor and secondary battery comprising same

Abstract

The present invention relates to a novel solid sodium ion conductor which can be used as an ion conductor, and a secondary battery comprising same. The solid ion conductor according to the present invention is represented by chemical formula 1. [Chemical formula 1] NaaZnbMcX4 (wherein M is at least one selected from among Ga, Al, In, Ca, and Ge, X is at least one selected from among S, Se, and I, 5.5≤a≤5.95, 0.5≤b≤1, and 0.05≤c≤0.6).

Description

Solid ion conductor and secondary battery containing the same

[0001] This invention was supported by the following national research and development project.

[0002] [Project ID] 1415184637

[0003] [Assignment Number] 20012196

[0004] Ministry of Trade, Industry and Energy

[0005] [Name of Project Management (Specialist) Institution] Korea Institute of Industrial Technology Planning and Evaluation

[0006] [Research Project Name] Industrial Technology Alchemist Project

[0007] [Research Project Name] AI-Based Supercritical Materials

[0008] The present invention relates to a novel sodium ion conductor having ion conductivity and a secondary battery including the same.

[0009] All-solid-state batteries (ASSBs) equipped with solid electrolytes (SSEs) can achieve higher operational safety and energy density than lithium-ion batteries (LIBs), which currently dominate the market. Therefore, the battery industry is actively conducting research to replace liquid-based electrolytes with solid electrolytes.

[0010] In the study of solid electrolytes, various types of Li-containing oxides, sulfides, and halides have been studied over the past several decades, and some of them have already reached ionic conductivities comparable to those of liquid electrolytes.

[0011] However, currently developed solid electrolyte materials do not have sufficient electrochemical stability when in contact with electrode materials, mainly during rest and / or charge / discharge cycles, and therefore are not applicable to practical all-solid-state batteries.

[0012] Recently, solid electrolyte materials with remarkable ionic conductivity have been discovered in the sodium sulfide series. For example, Na3-x Sb 1-x W x S4 and Na 3+x-y Sb 1-x-y Si x W y Materials such as S4 have a similar conductivity to liquid electrolytes, with a value of 10 mScm -1 Although these compounds exhibit high ionic conductivity, they have high valence W 6+ It is expected that the electrochemical stability will be low because it contains .

[0013] The purpose of the present invention is to provide a novel solid ion conductor composition having ion conductivity and applicable to an all-solid-state battery, and a secondary battery including the same.

[0014] One aspect of the present invention is to provide a solid ion conductor represented by the following chemical formula 1.

[0015] [Chemical Formula 1]

[0016] Na a Zn b M c X4

[0017] (M is at least one selected from Ga, Al, In, Ca, and Ge, and X is at least one selected from S, Se, and I, and 5.5≤a≤5.95, 0.5≤b≤1, 0.05≤c≤0.6)

[0018] Another aspect of the present invention provides a secondary battery comprising: a positive electrode; a negative electrode disposed opposite the positive electrode with a predetermined gap therebetween; and an electrolyte disposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode, or the electrolyte comprises a solid ion conductor according to one aspect of the present invention.

[0019] The solid ion conductor according to the present invention is a composition that is not known to be a sodium (Na) ion conductor to date.

[0020] Figure 1 is Na 6-x Zn 1-x Ga xXRD pattern of S4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5).

[0021] Figure 2 is Na synthesized according to Example 2. 5.8 Zn 0.8 Al 0.2 This is the XRD pattern of the S4 compound.

[0022] Figure 3 is Na synthesized according to Example 3. 5.8 Zn 0.8 In 0.2 This is the XRD pattern of the S4 compound.

[0023] Figure 4 is Na synthesized according to Example 4. 5.6 Ca 0.2 This is the XRD pattern of the ZnS4 compound.

[0024] Figure 5 is Na synthesized according to Example 5. 5.9 ZnS 3.9 I 0.1 This is the XRD pattern of the compound.

[0025] Figure 6 is Na synthesized according to Example 6. 5.6 Zn 0.6 Ga 0.4 This is the XRD pattern of the Se4 compound.

[0026] Figure 7 is Na synthesized according to Example 7. 5.8 Zn 0.9 Ge 0.1 This is the XRD pattern of the Se4 compound.

[0027] Figure 8 is Na synthesized according to Example 8. 5.9 ZnSe 3.9 I 0.1 This is the XRD pattern of the compound.

[0028] Figure 9 shows Na at room temperature 6-x Zn 1-x Ga x EIS spectrum and conductivity of S4(x = 0, 0.1, 0.2, 0.3, 0.4, 0.5).

[0029] Figure 10 is Na synthesized according to Example 2. 5.8 Zn 0.8 Al 0.2This is the EIS spectrum of the S4 compound.

[0030] Figure 11 is Na synthesized according to Example 3. 5.8 Zn 0.8 In 0.2 This is the EIS spectrum of the S4 compound.

[0031] Figure 12 is Na synthesized according to Example 4. 5.6 Ca 0.2 This is the EIS spectrum of the ZnS4 compound.

[0032] Figure 13 is Na synthesized according to Example 5. 5.9 ZnS 3.9 I 0.1 This is the EIS spectrum of the cargo.

[0033] Figure 14 is Na synthesized according to Example 6. 5.6 Zn 0.6 Ga 0.4 This is the EIS spectrum of the Se4 compound.

[0034] Figure 15 is Na synthesized according to Example 7. 5.8 Zn 0.9 Ge 0.1 This is the EIS spectrum of the Se4 compound.

[0035] Figure 16 is Na synthesized according to Example 8. 5.9 ZnSe 3.9 I 0.1 This is the EIS spectrum of the compound.

[0036] The terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his or her own invention.

[0037] Hereinafter, the present invention will be described in detail based on preferred embodiments thereof with reference to the attached drawings. The embodiments described in this specification and the configurations depicted in the drawings are merely preferred embodiments of the present invention and do not fully represent the technical ideas of the present invention. Therefore, various equivalents and modified examples may exist that can replace them at the time of this application, and the scope of the present invention is not limited to the embodiments described below.

[0038] One embodiment of the present invention is a solid ion conductor represented by the following chemical formula 1.

[0039] [Chemical Formula 1]

[0040] Na a Zn b M c X4

[0041] (M is at least one selected from Ga, Al, In, Ca, and Ge, and X is at least one selected from S, Se, and I, and 5.5≤a≤5.95, 0.5≤b≤1, 0.05≤c≤0.6)

[0042] The above a can be 5.5 to 5.95, 5.5 to 5.9, 5.5 to 5.85, 5.5 to 5.8, 5.5 to 5.75, 5.5 to 5.7, 5.5 to 5.65.

[0043] The above b can be 0.5 to 1, 0.55 to 1, or 0.6 to 1.

[0044] The above c may be 0.05 to 0.6, and preferably 0.1 to 0.5, 0.2 to 0.5, 0.3 to 0.5, or 0.35 to 0.45, as the ionic conductivity is too low when c is less than 0.05, and impurities may be introduced when c exceeds 0.6.

[0045] In the above solid ion conductor, M may be Ga and X may be S.

[0046] In the above solid ion conductor, M may be Ga and X may be Se.

[0047] The space group of the above solid ion conductor may be P63mc.

[0048] The above solid ion conductor may not include a Na2ZnS2 phase.

[0049] Another embodiment of the present invention is a secondary battery comprising a positive electrode, a negative electrode disposed opposite the positive electrode with a predetermined gap therebetween, and an electrolyte disposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode, or the electrolyte comprises a solid ion conductor according to one embodiment.

[0050] The above positive electrode, negative electrode and electrolyte may be applied in any possible form known in the secondary battery field, and may preferably be configured as an all-solid-state battery.

[0051]

[0052] <Example 1>

[0053] Na (metal), ZnS (purity 99.99%), Ga2Se3 (purity 99.99%), and S (purity 99.98%) were used as synthetic raw materials.

[0054] Na 6-x Zn 1-x Ga xIn order to synthesize a compound having the composition of S4 (x is 0, 0.1, 0.2, 0.3, 0.4, 0.5), the raw materials are weighed, and the sample is ground at a speed of 40 Hz for 5 minutes using a mini mill. Repeat this 6 times, and the sample is ground using a mini mill for a total of 30 minutes. The powdered sample is placed in a carbon crucible using a stainless steel spatula. At this time, slight pressure is applied with the stainless steel spatula so that the sample contained therein does not fall out even when the carbon crucible is tilted. The carbon crucible containing the sample is placed in a quartz tube, and the quartz tube is made into a vacuum. The quartz tube is placed in a box furnace (filled with Ar gas with an internal pressure of 2.0 to 4.0 mbar and a purity of 99.9%), heated to 550°C at a heating rate of 40°C / h, maintained for 12 hours, and then slowly cooled in the box furnace. When the temperature inside the box furnace drops below 50°C, the sample is taken out. Through the above process, Na 6-x Zn 1-x Ga x A compound having the composition S4 (x is 0, 0.1, 0.2, 0.3, 0.4, 0.5) was synthesized.

[0055]

[0056] <Example 2>

[0057] Na2S, ZnS (purity 99.99%), and Al2S3 (purity 99%) were used as synthetic raw materials.

[0058] Weigh the raw materials so that Na2S 0.4607g, ZnS 0.1587g, and Al2S3 0.0305g, and then transfer them to an agate mortar and grind them with an agate pestle for 15 minutes. Put the powdered sample into an alumina crucible using a stainless steel spatula. At this time, apply slight pressure with the stainless steel spatula so that the sample does not fall out even if the alumina crucible is tilted. Put the alumina crucible containing the sample into a quartz tube, and make the quartz tube into a vacuum. Put the quartz tube into a box furnace (internal pressure 2.0 to 4.0 mbar, filled with 99.9% pure Ar gas), heat to 650℃ at a heating rate of 5℃ / min, maintain for 12 hours, and then slowly cool in the box furnace. When the temperature inside the box furnace drops below 50℃, the sample is taken out. Through the above process, Na 5.8 Zn 0.8 Al 0.2 S4 was synthesized.

[0059]

[0060] <Example 3>

[0061] Na2S, ZnS (purity 99.99%), and In2S3 (purity 99.999%) were used as synthetic raw materials.

[0062] After weighing the raw materials to be Na2S 0.4031g, ZnS 0.1388g, In2S30.0580g, through the same process as Example 2, Na 5.8 Zn 0.8 In 0.2 S4 was synthesized.

[0063]

[0064] <Example 4>

[0065] Na2S, ZnS (purity 99.99%), and CaS (purity 99.9%) were used as synthetic raw materials.

[0066] After weighing the raw materials to be Na2S 0.3968g, ZnS 0.1769g, CaS 0.0262g, through the same process as Example 2, Na 5.6 Ca 0.2 ZnS4 was synthesized.

[0067]

[0068] <Example 5>

[0069] Na2S, ZnS (purity 99.99%), and NaI (purity 99%) were used as synthetic raw materials.

[0070] The raw materials were weighed to be 0.6681 g of Na2S, 0.2877 g of ZnS, and 0.0442 g of NaI, transferred to an agate mortar, and ground with an agate pestle for 20 minutes. The subsequent process was performed in the same manner as in Example 1 to obtain Na 5.9 ZnS 3.9 I 0.1 was synthesized.

[0071]

[0072] <Example 6>

[0073] Na (metal), Se (metal), ZnSe (purity 99.99%), and Ga2Se3 (purity 99.99%) were used as synthetic raw materials.

[0074] First, weigh out 0.3496g of Na and 0.6004g of Se, then add the cut Na metal to 0.3g of Se in an agate mortar, and use a stainless steel spatula to evenly spread Se on the surface of Na, then place it in a quartz tube, and make the inside of the quartz tube vacuum. Place the quartz tube in a box furnace, heat it to 550℃ at a heating rate of 5℃ / min, and maintain it for 24 hours. After gradually cooling it inside the box furnace, take out the sample when the temperature inside the box furnace drops below 50℃. Na2Se was synthesized through this process.

[0075] Next, weigh out 0.6837g of synthesized Na2Se, 0.1692g of ZnSe, and 0.1471g of Ga2Se3, and grind the sample using a mini-mill at a speed of 40Hz for 5 minutes. Repeat this process 6 times, grinding for a total of 30 minutes using a mini-mill. Put the powdered sample into a carbon crucible using a stainless steel spatula. At this time, apply slight pressure with the stainless steel spatula so that the sample does not fall out even if the carbon crucible is tilted. Put the carbon crucible containing the sample into a quartz tube, and make the quartz tube into a vacuum state. Put the quartz tube into a box furnace, heat to 550℃ at a heating rate of 5℃ / min, and maintain for 12 hours. Then, slowly cool the sample in the box furnace, and take out the sample when the temperature inside the box furnace drops below 50℃. Through the above process, Na 5.6 Zn 0.6 Ga 0.4 Se4 was synthesized.

[0076]

[0077] <Example 7>

[0078] Na (metal), Se (metal), ZnSe (purity 99.99%), and Ge (purity 99.999%) were used as synthetic raw materials.

[0079] First, Na2Se was synthesized using the same process as Example 6.

[0080] Next, after weighing 0.7032 g of Na2Se, 0.2521 g of ZnSe, 0.0141 g of Ge, and 0.0306 g of Se, the same process as Example 6 was performed. 5.8 Zn 0.9 Ge 0.1 Se4 was synthesized.

[0081]

[0082] <Example 8>

[0083] Na (metal), Se (metal), ZnSe (purity 99.99%), and NaI (purity 99%) were used as synthetic raw materials.

[0084] First, Na2Se was synthesized using the same process as Example 6.

[0085] Next, weigh out 0.3473g of Na2Se, 0.1383g of ZnSe, and 0.0144g of NaI, then transfer the weighed raw materials to an agate mortar and grind them with an agate pestle for 15 minutes. Put the powdered sample into an alumina crucible using a stainless steel spatula. At this time, apply slight pressure with the stainless steel spatula so that the sample does not fall out even if the alumina crucible is tilted. Put the alumina crucible containing the sample into a quartz tube, and make the quartz tube into a vacuum state. Put the quartz tube into a box furnace, heat it to 550℃ at a heating rate of 5℃ / min, maintain it for 12 hours, and then slowly cool it in the box furnace. When the temperature inside the box furnace drops below 50℃, take out the sample. Through this process, Na 5.9 ZnSe 3.9 I 0.1 was synthesized.

[0086]

[0087] Crystal structure analysis

[0088] X-ray diffraction analysis was performed on the compounds synthesized according to Examples 1 to 8.

[0089] Figure 1 is Na 6-x Zn 1-x Ga x XRD pattern of S4 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5). As confirmed in Fig. 1, Ga 3+ is an impurity detected in undoped Na6ZnS4. The Na2ZnS2 phase was not detected in the compounds of x = 0.1, 0.2, 0.3, 0.4, and 0.5. In addition, Na 6-x Zn 1-x Ga xThe XRD patterns of S4 (x = 0.1, 0.2, 0.3, 0.4, 0.5) were almost identical to the standard pattern of Na6ZnS4 (space group = P63mc, ICSD 34525). In the sample with x = 0.5, a small amount of Na6ZnS4 and Na5GaS4 impurity phases were detected. Therefore, x less than 0.5 may be preferable.

[0090] Figures 2 to 8 are XRD patterns of compounds synthesized according to Examples 2 to 8, respectively. Na synthesized according to Example 2 5.8 Zn 0.8 Al 0.2 S4, Na synthesized according to Example 3 5.8 Zn 0.8 In 0.2 S4, Na synthesized according to Example 4 5.6 Ca 0.2 ZnS4 and Na synthesized according to Example 5 5.9 ZnS 3.9 I 0.1 In the case of , the main phase contains some impurities, but the main phase has a crystal structure that matches the Na6ZnS4 phase. In addition, Na synthesized according to Example 6 5.6 Zn 0.6 Ga 0.4 Se4, Na synthesized according to Example 7 5.8 Zn 0.9 Ge 0.1 Na synthesized according to Se4 and Example 8 5.9 ZnSe 3.9 I 0.1 The compound has a crystal structure consistent with the Na6ZnSe4 phase, although the main phase contains some impurities.

[0091]

[0092] ionic conductivity

[0093] To measure the ionic conductivity of the synthesized compound, the synthesized powder was manually ground for more than 20 minutes, and then the powder was compressed at a pressure of 4T (350 MPa) or less to produce pellets.

[0094] Electrochemical impedance spectroscopy (EIS) spectra were measured for pellets sandwiched between In foils while applying an AC voltage of 10 mV.

[0095] Figure 9 shows Na at room temperature 6-x Zn 1-x Ga x EIS spectra and conductivity of S4(x = 0, 0.1, 0.2, 0.3, 0.4, 0.5). As confirmed in Fig. 9, for undoped Na6ZnS4, the EIS spectrum is Na + The conduction was negligible, and the resistance was approximately 190 MΩ, indicating insulating properties. In comparison, Na 6-x Zn 1-x Ga x Ga as S4(x = 0.1, 0.2, 0.3, 0.4, 0.5) 3+ For the doped compound, the resistance is reduced to the kΩ level, indicating that it can be used as an ionic conductor. 3+ As the doping amount increased, the resistance decreased, but Ga 3+ When the doping amount is 0.5, the resistance tends to increase, which seems to be due to the impurities generated as the doping amount increases. Therefore, Ga 3+ The doping amount is preferably 0.3 to 0.5, and more preferably 0.35 to 0.45.

[0096] Figures 10 to 16 are EIS spectra of compounds synthesized according to Examples 2 to 8, and Table 1 below summarizes the results.

[0097] Sample composition conductivity (μS·cm) -1) Resistance (kΩ) Example 2Na 5.8 Zn 0.8 Al 0.2 S40.15320 Example 3Na 5.8 Zn 0.8 In 0.2 S40.483100 Example 4Na 5.6 Ca 0.2 ZnS40.337150Example 5Na5.9 ZnS 3.9 I 0.1 0.022646 Example 6Na 5.6 Zn 0.6 Ga 0.4 Se4211.9 Example 7Na 5.8 Zn 0.9 Ge 0.1 Se40.094425 Example 8Na 5.9 ZnSe 3.9 I 0.1 0.014019

[0098] As shown in Table 1, Examples 2 to 8 all exhibited ionic conductivity, confirming their potential as materials applicable to solid ionic conductors. Among them, the conductivity of compounds doped with Al, In, Ca, and Ge was relatively higher, and the conductivity of Example 6 was the highest.

Claims

1. A solid ion conductor represented by the following chemical formula 1. [Chemical Formula 1] On a Zn b M c X 4 (M is at least one selected from Ga, Al, In, Ca, and Ge, and X is at least one selected from S, Se, and I, and 5.5≤a≤5.95, 0.5≤b≤1, 0.05≤c≤0.6) 2. In paragraph 1, A solid ionic conductor wherein M is Ga and X is S.

3. In paragraph 1, A solid ionic conductor wherein M is Ga and X is Se.

4. In paragraph 1 or 2, A solid ionic conductor, wherein c is 0.3 to 0.

5.

5. In any one of paragraphs 1 to 3, A solid ionic conductor whose space group is P63mc.

6. In any one of paragraphs 1 to 3, A solid ionic conductor, wherein c is 0.35 to 0.

45.

7. In paragraph 2, The above solid ion conductor is Na 2 ZnS 2 A solid ionic conductor, not including a phase.

8. Bipolar, A cathode and a positive electrode are positioned opposite each other at a predetermined distance from each other. Containing an electrolyte disposed between the positive and negative electrodes, A secondary battery, wherein at least one of the positive electrode, negative electrode, or electrolyte comprises a solid ion conductor as described in any one of claims 1 to 3 and claim 7.

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