Lithium secondary battery having low-humidity oxidation coating layer, all-solid-state secondary battery, and method for manufacturing lithium secondary battery having low-humidity oxidation coating layer

Abstract

Disclosed are a lithium secondary battery having a low-humidity oxidation coating layer, the battery having a lithium metal negative electrode oxidized at low humidity to improve the performance and lifespan of a cell due to the LiOH and Li2O coating layer formed on the surface of the lithium metal negative electrode, an all-solid-state secondary battery, and a method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer. The method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer of the present invention comprises: a first step (S10) of preparing a lithium negative electrode by cutting lithium foil; a second step (S20) of exposing the lithium metal negative electrode to air having a temperature of 20°C to 25°C and a humidity of 15% to 25%; and a third step (S30) of depositing an amorphous metal alloy on the surface of the lithium metal negative electrode obtained in the second step (S20) to a thickness of 10 μm to 15 μm by means of sputtering.

Description

Lithium secondary battery having a low-humidity oxidation coating layer, all-solid-state secondary battery, and method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer

[0001] The present invention relates to a lithium secondary battery having a low-humidity oxidation coating layer, an all-solid-state secondary battery, and a method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer, and more particularly, to a lithium secondary battery having a low-humidity oxidation coating layer including a lithium metal negative electrode oxidized at low humidity, and a method for manufacturing a lithium secondary battery having an all-solid-state secondary battery and a low-humidity oxidation coating layer.

[0002] Lithium secondary batteries are batteries that generate electrical energy through changes in chemical potential when lithium ions intercalate / deintercalate at the positive and negative electrodes. The operating voltage and energy density of lithium secondary batteries can vary depending on factors such as the electrode active material, the type of electrolyte, and the loading amount of the electrode mixture layer. Examples of positive active materials include lithium-cobalt composite oxides and lithium-containing manganese composite oxides, while negative active materials include lithium metal, carbon-based materials, and silicon.

[0003] When lithium metal is used as the cathode, lithium dendrites form on the surface of the lithium metal during the battery's charge and discharge process. If these dendrites grow and penetrate the separator, microscopic shorts can occur, shortening the lifespan of the lithium secondary battery and posing a critical safety risk. Research is needed to suppress the growth of lithium dendrites and improve cell performance and lifespan.

[0004] The invention aims to solve the above problems by providing a lithium secondary battery having a low-humidity oxidation coating layer, which improves the performance and lifespan of the cell by LiOH and Li2O coating layers formed on the surface of the lithium metal negative electrode, and a method for manufacturing a lithium secondary battery having an all-solid-state secondary battery and a low-humidity oxidation coating layer, by including a lithium metal negative electrode oxidized at low humidity.

[0005] In order to achieve the above-mentioned purpose, the lithium secondary battery of the present invention comprises: a positive electrode; a lithium metal negative electrode facing the positive electrode; an electrolyte positioned between the positive electrode and the negative electrode; a separator separating the positive electrode and the negative electrode; and a low-humidity oxide coating layer on one surface of the lithium metal negative electrode.

[0006] The lithium secondary battery of the present invention comprises: a positive electrode; a lithium metal negative electrode facing the positive electrode; an electrolyte positioned between the positive electrode and the negative electrode; and a low-humidity oxide coating layer on one surface of the lithium metal negative electrode.

[0007] In addition, in order to achieve the above-mentioned purpose, the method for manufacturing a lithium secondary battery having a low-humidity oxide coating layer of the present invention includes a first step of preparing a lithium metal negative electrode by cutting lithium foil; and a second step of forming a low-humidity oxide coating layer by exposing the lithium metal negative electrode to air at a temperature of 20°C to 25°C and a humidity of 15% to 25%.

[0008] In the second step, the time for exposing the lithium metal negative electrode to air is preferably 10 to 120 minutes, and more preferably, the time for exposing the lithium metal negative electrode to air is preferably 50 to 110 minutes.

[0009] In addition, in order to achieve the above-described object, the method for manufacturing a lithium secondary battery having a low-humidity oxide coating layer of the present invention includes a first step of preparing a lithium metal negative electrode by cutting lithium foil; a second step of forming a low-humidity oxide coating layer by exposing the lithium metal negative electrode to air at a temperature of 20° C. to 25° C. and a humidity of 15% to 25%; and a third step of forming an amorphous metal alloy layer by sputtering on one surface of the low-humidity oxide coating layer of the second step to form an amorphous metal alloy layer.

[0010] In the second step, the time for exposing the lithium metal negative electrode to air is preferably 60 to 120 minutes, and more preferably, the time for exposing the lithium metal negative electrode to air is preferably 70 to 110 minutes.

[0011] In addition, in order to achieve the above-described object, the method for manufacturing a lithium secondary battery having a low-humidity oxide coating layer of the present invention includes a first step of preparing a lithium metal negative electrode by cutting lithium foil; a second step of forming a low-humidity oxide coating layer by depositing a target mixed powder composed of LiOH and Li2O in a vacuum to a thickness of 5 nm to 500 nm on the surface of the lithium metal negative electrode by sputtering; and a third step of depositing an amorphous metal alloy to a thickness of 10 nm to 15 nm on the surface of the lithium metal negative electrode of the second step by sputtering.

[0012] In addition, the low-humidity oxidation coating layer comprises 20 to 60 wt% of LiOH, 20 to 60 wt% of Li2O, and 5 to 20 wt% of Li2CO3. More preferably, the low-humidity oxidation coating layer comprises 30 to 50 wt% of LiOH, 30 to 50 wt% of Li2O, and 5 to 10 wt% of Li2CO3.

[0013] In addition, the low-humidity oxidation coating layer comprises 20 to 80 wt% of LiOH and 20 to 80 wt% of Li2O. More preferably, the low-humidity oxidation coating layer comprises 30 to 70 wt% of LiOH and 30 to 70 wt% of Li2O. In addition, the low-humidity oxidation coating layer comprises less than 35 wt% of Li2CO.

[0014] The thickness of the low-humidity oxidation coating layer is preferably 5 nm to 500 nm, and more preferably, the thickness of the low-humidity oxidation coating layer is preferably 5 nm to 100 nm.

[0015] An amorphous metal is deposited on one surface of the above low-humidity oxide coating layer to further form an amorphous metal alloy layer having a thickness of 10 nm to 15 nm, and more preferably, an amorphous metal alloy layer having a thickness of 10 nm to 13 nm is formed.

[0016] The above amorphous metal alloy layer is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), promethium (Pm), samarium (Sm), lutetium (Lu), yttrium (Y), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), hormium (Ho), erbium (Er), thulium (Tm), thorium (Th), calcium (Ca), scandium (Sc), barium (Ba), beryllium (Be), bismuth (Bi), germanium (Ge), lead (Pb), ytterbium (Yb), strontium (Sr), europium (Eu), zirconium (Zr), thallium (Tl), lithium (Li), hafnium (Hf), One or a mixture of two or more selected from magnesium (Mg), phosphorus (P), arsenic (As), palladium (Pd), gold (Au), plutonium (Pu), gallium (Ga), germanium (Ge), aluminum (Al), copper (Cu), zinc (Zn), antimony (Sb), silicon (Si), tin (Sn), titanium (Ti), cadmium (Cd), indium (In), platinum (Pt), and mercury (Hg) amorphous metals is used. More preferably, the amorphous metal alloy layer uses a Zr-based amorphous metal alloy layer.

[0017] As described above, the present invention has the effect of improving the performance and lifespan of a cell by forming LiOH and Li2O coating layers on a lithium metal negative electrode through low-humidity oxidation to prevent lithium from growing in the form of dendrite.

[0018] Figure 1 is a flow chart of a method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer according to a third embodiment of the present invention.

[0019] Figure 2 is a flowchart of a method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer according to the fourth embodiment of the present invention.

[0020] Figure 3(a) shows that when bare lithium is used, the current is concentrated and the lithium that is plated grows in the form of dendrites, and Figure 3(b) shows that the thin LiOH and Li2O layers on the surface of the lithium prevent the lithium from growing in the form of dendrites and induce the lithium to grow evenly.

[0021] Fig. 4(a) shows that as oxidation progresses, Li2CO3 is generated on the surface, and Li2CO3 prevents lithium plating, and Fig. 4(b) shows that by depositing 12ZrMG on the surface, a thin Li2CO3 layer is removed, allowing lithium to be evenly plated.

[0022] Figure 5 shows the relationship between the cycle number, discharge capacity, and coulombic efficiency of a full cell during low-humidity oxidation.

[0023] Figure 6(a) shows the capacity-to-voltage relationship of a full cell under low-humidity oxidation after 1 cycle, and Figure 6(b) shows the capacity-to-voltage relationship of a full cell under low-humidity oxidation after 5 cycles.

[0024] Figure 7 shows the relationship between the cycle number and discharge capacity of a full cell during high humidity oxidation.

[0025] Figure 8 shows the relationship between voltage and time (overpotential) of a full cell during low-humidity oxidation.

[0026] Figure 9(a) shows XPS at a depth of 0 nm from the electrode surface during low-humidity oxidation, Figure 9(b) shows XPS at a depth of 20 nm from the electrode surface during low-humidity oxidation, and Figure 9(c) shows XPS at a depth of 150 nm from the electrode surface during low-humidity oxidation.

[0027] Figure 10 shows the number of oxygen (O) and carbon (C) per 100 lithium using atomic % by element.

[0028] The present invention is susceptible to various modifications and embodiments. Specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention. Throughout the description of each drawing, similar reference numerals have been used to designate similar components.

[0029] Terms such as first, second, A, and B may be used to describe various components, but these components should not be limited by these terms. These terms are used solely to distinguish one component from another.

[0030] For example, without departing from the scope of the present invention, the first component could be referred to as the second component, and similarly, the second component could also be referred to as the first component. The term "and / or" includes any combination of a plurality of related listed items or any one of a plurality of related listed items.

[0031] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0032] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0033] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0034]

[0035] (Experimental Example 1) Comparison of cell cycle performance (capacity per cycle)

[0036] 1. Cathode production

[0037] The electrodes were fabricated by cutting 200 μm thick lithium foil into 16 mm in diameter and exposing it to air at a temperature (25°C) and humidity (20%) for a certain period of time. Then, 12ZrMG deposition was performed by depositing 12 nm of Zr-based metallic glass on a lithium disk using a magnetron sputtering. Sputtering was performed at DC 125 W for 45 seconds, and sputtering was performed in an Ar (99.999%) 5x10 -5 It was conducted in a Torr environment.

[0038] 2. Cell production

[0039] CR2032 coin cells were used for full cell fabrication, and the cells were manufactured in a glove box under an Ar atmosphere (O2 < 1 ppm, H2O < 1 ppm). The electrolyte used was 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which was used in a 1:1 weight ratio of 1,3-dioxolane / 1,2-dimethoxyethande (DOL / DME) containing 2 wt% lithium nitrate (LiNO3), and the cathode had a capacity of 1.5 mAh / cm 2 LiFePO4 (LFP: Super P: PVDF = 8:1:1) was used. The full cell was manufactured in the following order: case, negative electrode (lithium metal with a diameter of 16 mm), separator (Celgard 2400), 70 μL electrolyte, gasket, positive electrode (LFP with a diameter of 14 mm), spacer, wave spring, and cap.

[0040] 3. Cell test conditions

[0041] Full cell testing was performed at a rate of 1.0 C and a voltage range of 3.0 V to 3.8 V.

[0042] 4. Conclusion

[0043] Fig. 3(a) shows that when bare lithium is used, lithium that is plated due to the concentrated current grows in the form of dendrites, and Fig. 3(b) shows that thin LiOH and Li2O layers on the surface of lithium prevent lithium from growing in the form of dendrites and induce lithium to grow evenly. As shown in Fig. 3(a), when bare lithium is used, lithium that is plated due to the concentrated current grows in the form of dendrites on the electrode surface. On the other hand, as shown in Fig. 3(b), thin LiOH and Li2O layers formed on the lithium metal prevent lithium from growing in the form of dendrites on the electrode surface.

[0044] Fig. 4(a) shows that as oxidation progresses, Li2CO3 is generated on the surface, and Li2CO3 hinders lithium plating, and Fig. 4(b) shows that when 12ZrMG is deposited on the surface, the thin Li2CO3 layer is removed, and lithium is evenly plated. Referring to Fig. 4(a), when oxidation continues to progress, Li2CO3 is mainly generated on the electrode surface, and Li2CO3 hinders lithium plating. However, when 12ZrMG is deposited on the surface of the electrode, as shown in Fig. 4(b), the thin Li2CO3 layer is removed, and lithium is evenly plated.

[0045] Figure 5 shows the relationship between the cycle number, discharge capacity, and coulombic efficiency of a full cell during low-humidity oxidation. Referring to Figure 5, when oxidation was performed at a temperature of 25°C and a humidity of 20%, cell performance increased with oxidation time, and in the case of bare lithium, performance was the best when exposed to air for 100 minutes. In addition, when 12ZrMG was deposited on the surface of the electrode, the cell lifespan was further increased.

[0046]

[0047] (Experimental Example 2) Comparison of cell cycle performance (voltage change during charge / discharge)

[0048] 1. Cell production

[0049] The electrode was fabricated by depositing 12ZrMG and exposed to air in an environment of 25℃ and 20% humidity, and 1.5 mAh / cm 2 A full cell was manufactured with LFP of capacity.

[0050] 2. Cell test conditions

[0051] The voltage profiles were compared by charging / discharging at a rate of 1.0 C and in the range of 3.0 V to 3.8 V.

[0052] 3. Conclusion

[0053] Fig. 6(a) shows the capacity-to-voltage relationship of a full cell under low-humidity oxidation after 1 cycle, and Fig. 6(b) shows the capacity-to-voltage relationship of a full cell under low-humidity oxidation after 5 cycles. Referring to Fig. 6(a) and Fig. 6(b), the full-cell test results under low-humidity oxidation (temperature 25℃, humidity 20%) show that the bare lithium has the best performance at 100 minutes, and the 12ZrMG electrode surface is coated at 80 minutes. That is, the voltage gap between the bare lithium exposed for 100 minutes and the 12ZrMG exposed for 80 minutes, which has the best performance, is smaller than that of the other cells, which indicates that the resistance is smaller than that of the other cells.

[0054]

[0055] (Comparative Example 1) Comparison of cell cycle performance (capacity per cycle)

[0056] 1. Cathode production

[0057] The electrodes were fabricated by cutting 200 μm thick lithium foil into 16 mm in diameter and exposing it to air at 25°C and 40% humidity for a certain period of time. Then, 12ZrMG deposition was performed by depositing 12 nm of Zr-based metallic glass on a lithium disk using a magnetron sputtering. Sputtering was performed at DC 125 W for 45 seconds, and sputtering was performed in an Ar (99.999%) 5x10 -5 It was conducted in a Torr environment.

[0058] 2. Cell production

[0059] CR2032 coin cells were used for full cell fabrication, and the cells were manufactured in a glove box under an Ar atmosphere (O2 < 1 ppm, H2O < 1 ppm). The electrolyte used was 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which was used in a 1:1 weight ratio of 1,3-dioxolane / 1,2-dimethoxyethande (DOL / DME) containing 2 wt% lithium nitrate (LiNO3), and the cathode had a capacity of 1.5 mAh / cm 2 LiFePO4 (LFP: Super P: PVDF = 8:1:1) was used. The full cell was manufactured in the following order: case, negative electrode (lithium metal with a diameter of 16 mm), separator (Celgard 2400), 70 μL electrolyte, gasket, positive electrode (LFP with a diameter of 14 mm), spacer, wave spring, and cap.

[0060] 3. Cell test conditions

[0061] Full cell testing was performed at a rate of 1.0 C and a voltage range of 3.0 V to 3.8 V.

[0062] 4. Conclusion

[0063] Figure 7 shows the relationship between the cycle count and discharge capacity of a full cell under high-humidity oxidation. Referring to Figure 7, when oxidation was performed at 25°C and 40% humidity, cell performance decreased with increasing air exposure time for bare lithium. However, after 3 minutes of exposure to air and subsequent deposition of 12ZrMG, cell performance increased again.

[0064]

[0065] (Experimental Example 3) Measurement of the energy required for lithium plating

[0066] 1. Cell production

[0067] A symmetric cell was fabricated using an electrode fabricated by depositing 12ZrMG as a working electrode and bare lithium as a counter electrode, exposed to air in an environment of 25℃ and 20% humidity.

[0068] 2. Cell test conditions

[0069] 0.1 mA / cm 2 and a rate of 0.5 mAh / cm 2 The overpotential was compared by charging / discharging at a rate of .

[0070] 3. Conclusion

[0071] Figure 8 shows the relationship between voltage and time (overpotential) of a full cell under low-humidity oxidation. Referring to Figure 8, it can be seen that the overall potential is lower for bare lithium exposed to 100 minutes than for cells not exposed to air. In other words, it can be seen that less energy is required to plate lithium metal exposed to 100 minutes. When 12ZrMG is deposited, the initial potential is high due to the potential caused by nucleation, but the potential gradually decreases thereafter and becomes lower than that of other cells. In other words, the growth potential is reduced when 12ZrMG is deposited.

[0072]

[0073] (Experimental Example 4) Substances affecting cycle performance

[0074] The electrodes fabricated by exposing them to air in an environment of 25℃ and 20% humidity and depositing 12ZrMG were analyzed by XPS.

[0075] Fig. 9(a) shows XPS at a depth of 0 nm from the electrode surface during low-humidity oxidation, Fig. 9(b) shows XPS at a depth of 20 nm from the electrode surface during low-humidity oxidation, and Fig. 9(c) shows XPS at a depth of 150 nm from the electrode surface during low-humidity oxidation. Referring to Figs. 9(a) to 9(c), XPS measurements were performed for three cases: bare lithium exposed for 0 min, bare lithium exposed for 100 min, and 12ZrMG exposed for 80 min to determine which substances affect cell performance during lithium oxidation. It should be noted that high-humidity oxidation inevitably occurs during the XPS sampling process. In the case of 0 min of exposure where only high-humidity oxidation occurred, no Li2O peak was detected. In other words, it can be confirmed that Li2O is not generated when Li2CO3 is generated due to high-humidity oxidation. On the other hand, Li2O peaks were detected in the case of 12ZrMG exposed for 100 minutes and 80 minutes under low-humidity (20% humidity) oxidation. In other words, it can be confirmed that Li2CO3 is not generated during low-humidity oxidation, but only Li2O and LiOH are generated.

[0076] Figure 10 shows the number of oxygen (O) and carbon (C) per 100 lithium using the atomic % of each element. Referring to Figure 10, in the case of 0 minutes when only high humidity (40% humidity) oxidation was performed, the oxygen (O) tends to continuously decrease, but in the case of 100 minutes of exposure when low humidity (20% humidity) oxidation was performed, it can be confirmed that the amount of oxygen (O) increases for a certain period of time and then decreases. Based on Figure 8, it can be estimated that the low-humidity oxidation coating layer containing Li2O and LiOH generated by low-humidity oxidation is approximately 20 nm.

[0077]

[0078] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Bipolar; A lithium metal negative electrode facing the positive electrode; An electrolyte positioned between the anode and cathode; A separator separating the positive and negative electrodes; and A lithium secondary battery having a low-humidity oxidation coating layer on one surface of the lithium metal negative electrode.

2. Bipolar; A lithium metal negative electrode facing the positive electrode; An electrolyte positioned between the anode and cathode; and A lithium secondary battery having a low-humidity oxidation coating layer on one surface of the lithium metal negative electrode.

3. In claim 1 or 2, A lithium secondary battery, characterized in that the low-humidity oxidation coating layer contains 20 to 60 wt% of LiOH, 20 to 60 wt% of Li2O, and 5 to 20 wt% of Li2CO3.

4. In claim 1 or 2, A lithium secondary battery, characterized in that the thickness of the low-humidity oxidation coating layer is 5 nm to 500 nm.

5. In claim 1 or 2, A lithium secondary battery characterized in that an amorphous metal is deposited on one surface of the low-humidity oxidation coating layer to further form an amorphous metal alloy layer having a thickness of 10 nm to 15 nm.

6. In claim 5, A lithium secondary battery, characterized in that the above amorphous metal alloy layer is a Zr-based amorphous metal alloy layer.

7. A method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer, Step 1: preparing a lithium metal negative electrode by cutting lithium foil; and A method for manufacturing a lithium secondary battery having a low-humidity oxide coating layer, comprising: a second step of forming a low-humidity oxide coating layer by exposing the lithium metal negative electrode to air at a temperature of 20°C to 25°C and a humidity of 15% to 25%.

8. A method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer, Step 1: preparing a lithium metal negative electrode by cutting lithium foil; A second step of forming a low-humidity oxide coating layer by exposing the lithium metal negative electrode to air at a temperature of 20°C to 25°C and a humidity of 15% to 25%; and A method for manufacturing a lithium secondary battery having a low-humidity oxide coating layer, comprising: a third step of forming an amorphous metal alloy layer by sputtering to deposit an amorphous metal alloy with a thickness of 10 nm to 15 nm on one surface of the low-humidity oxide coating layer of the second step; 9. In claim 8, A method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer, characterized in that the time for exposing the lithium metal negative electrode to air in the second step is 10 to 120 minutes.

10. A method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer, Step 1: preparing a lithium metal negative electrode by cutting lithium foil; A second step of forming a low-humidity oxide coating layer by sputtering and depositing a target mixed powder composed of LiOH and Li2O in a vacuum to a thickness of 5 nm to 500 nm on the surface of the lithium metal negative electrode; and A method for manufacturing a lithium secondary battery having a low-humidity oxidation coating layer, comprising: a third step of depositing an amorphous metal alloy with a thickness of 10 nm to 15 nm on the surface of the lithium metal negative electrode of the second step by sputtering;

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