WO2018105807A1 - Method for manufacturing anode for lithium secondary battery, anode for lithium secondary battery manufactured by using same method and lithium secondary battery comprising same anode - Google Patents

Abstract

The present specification relates to a method for manufacturing an anode for a lithium secondary battery, comprising the steps of: forming an anode active material layer by coating an anode active material on a current collector; and coating a protective film on the anode active material layer, wherein the step of coating the protective film uses a thermal deposition process.

Description

 [Specifications

 [Name of invention]

 Method for manufacturing a negative electrode for a lithium secondary battery, a negative electrode for a lithium secondary battery manufactured using the same and a lithium secondary battery comprising the same

 [Technical Field]

 The present disclosure relates to a method of manufacturing a negative electrode for a lithium secondary battery, a lithium secondary battery negative electrode manufactured using the same, and a lithium secondary battery including the same.

 [Background technology]

 Recently, lithium secondary batteries are receiving attention as power sources for driving portable electronic devices and electric vehicles. This is because the use of the organic electrolyte can exhibit a higher discharge voltage and higher power than the battery using the conventional aqueous alkali solution and can exhibit high power.

 Lithium secondary batteries mounted in electric vehicles, etc. need to increase energy density through weight reduction and volume reduction. To this end, development of a negative electrode material using lithium continues.

 Lithium anode material capacity is approximately compared to carbon-based anode material capacity of 370 mAh / g

~ 3, 860mAh / g, can have a theoretical capacity close to 10 times. In addition, the thickness of the negative electrode including the carbon-based negative electrode material is about 50 to 60 um, the thickness of the negative electrode including the lithium negative electrode material is about 5 to 20um. Therefore, in the case of including a lithium material, the volume of the lithium secondary battery may be reduced by 1/3 or more.

 However, when lithium is used as a negative electrode material, 1) dendrites are formed, 2) dead lithium is generated, and 3) volume is expanded.

During the charge and discharge process of high current density, lithium dendrites are generated on the surface of the lithium anode. Such lithium dendrites may penetrate the separator to cause a short with the positive electrode, or due to an increase in the surface area, a continuous formation of a thin film (SEI) due to reaction between the negative electrode and the electrolyte may cause electrolyte depletion and cause generation of dead lithium. Can be. This reduces the cycle efficiency of the battery. In the case of replacing the carbon-based negative electrode material with lithium in a lithium ion battery, the energy density per weight and volume can be increased, but it is necessary to suppress the formation of lithium dendrites formed during layer formation and discharge.

 [Detailed Description of the Invention]

 [Technical problem]

 The present invention is to provide a method for producing a negative electrode for a lithium secondary battery comprising a protective film to suppress the formation of lithium dendrites, a negative electrode for a lithium secondary battery prepared therefrom and a lithium secondary battery comprising the same.

 In addition, the technical problem to be solved by the present invention is not limited to the technical problem mentioned above, and other technical problems not mentioned are clearly to those of ordinary skill in the art from the following description. It can be understood.

 Technical Solution

 Coating the negative electrode active material on the current collector according to an embodiment of the present invention to form a negative electrode active material layer, and coating a protective film on the negative electrode active material layer, and coating the protective film using a thermal deposition process .

 The protective film may be formed to a thickness of about 10 nm to about 500 nm. At least one of the forming of the anode active material layer and the forming of the protective film may be performed in a vacuum.

 The forming of the passivation layer may be performed by opening the chamber. The current collector may be at least one selected from the group consisting of copper, gold, nickel and alloys thereof.

 The negative electrode active material may be at least one selected from the group consisting of lithium, a lithium alloy, and a carbon material.

 The protective film may be lithium halide.

 The negative electrode active material layer may be formed using a first boat, the protective layer may be formed using a second boat, and a partition wall may be positioned between the first boat and the second boat.

The negative electrode active material charge may be in direct contact with the protective film. A negative electrode for a rechargeable lithium battery according to one embodiment may be manufactured using the above-described method.

 The lithium secondary battery according to an embodiment may include a cathode, an anode, and a separator positioned between the cathode and the anode, and the anode may be manufactured using the above-described method.

 【Effects of the Invention】

 According to the above-described embodiment, it is possible to provide a method for manufacturing a negative electrode for a lithium secondary battery in which a protective film is uniformly formed, and the negative electrode and lithium secondary battery manufactured therefrom suppress lithium dendrite formation and have a layer discharge life of the battery. Can be increased.

 [Brief Description of Drawings]

 1 is a schematic cross-sectional image of a negative electrode for a lithium secondary battery according to the present invention.

 2 is a schematic cross-sectional image according to the method of manufacturing a negative electrode for a lithium secondary battery of the present invention.

 FIG. 3 is a graph showing the results of the full stripping test of Example 1. FIG.

 4 to 10 are graphs of layer discharge / discharge evaluations of batteries according to Examples and Comparative Examples.

 11 to 13 illustrate ESCA depths according to Examples and Comparative Examples.

Depth Profile measurement graph.

 [Best form for implementation of the invention]

 Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, in describing the present disclosure, description of the already known function or configuration will be omitted to clarify the gist of the present disclosure.

Parts not related to the description are omitted for clarity of description, and like reference numerals designate like elements throughout the specification. In addition, the size and thickness of each configuration shown in the drawings are arbitrarily shown for convenience of description The description is not necessarily limited to what is shown.

 In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. In the drawings, the thicknesses of some layers and regions are exaggerated for convenience of explanation. When a part of a layer, film, area, plate, etc. is said to be "on" or "on" another part, this includes not only the other part "on top" but also another part in the middle.

 Lithium secondary batteries can be classified into lithium ion batteries (hereinafter referred to as "lithium secondary batteries"), lithium ion polymer batteries and lithium polymer batteries according to the type of separator and electrolyte used. It can be classified into doll, pouch type, etc., and can be divided into bulk type and thin film type according to the size. Since the structure and manufacturing method of these batteries are well known in the art, detailed description thereof will be omitted.

 More specifically, the lithium secondary battery may be configured by sequentially stacking a negative electrode, a positive electrode, and a separator, and then storing the lithium secondary battery in a battery container in a state of being wound on a spiral.

 The negative electrode may include a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer may include a negative electrode active material. Specifically, the negative electrode according to an embodiment of the present invention may include a current collector, a negative electrode active material layer formed on the current collector, a protective film formed on the negative electrode active material layer.

 The negative electrode according to an embodiment may be manufactured by coating a negative electrode active material on a current collector to form a negative electrode active material layer, and forming a protective film on the negative electrode active material layer.

Negative electrode current collector include copper, gold, nickel, ^"and can include but at least one selected from the group consisting of alloys thereof, but is not limited thereto.

 As the negative electrode active material, lithium ions are reversibly

Intercalation / de-intercalable material may be at least one selected from the group comprising lithium, lithium alloys, carbon materials, materials doped and undoped in lithium, and transition metal oxides.

The method of forming the negative electrode active material layer is a method of directly depositing a negative electrode active material on a current collector A coating method may be used, and the present invention is not limited thereto, and a method of coating a negative active material on a separate support and drying the film, and then laminating the film obtained by peeling from the support may be used on a current collector.

The support may be any material capable of supporting the negative electrode active material layer, and may be, for example, a mylar film or a polyethylene terephthalate (PET) film.

 The protective film may include lithium halide, for example

Lithium fluoride (LiF). Lithium halides have a large band gap and are commonly used in UV opt ics, and have a low melting point of 845 ° C., and may be suitable for vacuum thermal evaporation.

 The protective film according to an embodiment may be formed to have a uniform thickness using a thermal deposition process. The protective film may be uniformly formed to a thickness of about 10 nra to about 500 nm. The protective film may be in direct contact with the negative electrode active material layer, and no foreign material or a foreign material layer may be disposed between the protective film and the negative electrode active material layer.

 The protective film prevents deterioration of the battery performance due to the formation of lithium dendrites, stably expresses high capacity characteristics even after repeated layer discharge, and provides a lithium secondary battery having excellent life characteristics and stability.

 The forming of the passivation layer may use a thermal deposition process. The thermal deposition process may be performed under the same conditions or not the same as the step of forming the negative electrode active material according to the embodiment. For example, the thermal deposition process in a vacuum state is advantageous in controlling the thickness and surface of the protective film, and the manufacturing process may be simple.

When the protective film is formed in a non-vacuum state, the lithium thin film may react with nitrogen, oxygen, fine moisture, and the like in the air to form a film such as Li ₃ N, LiOH, Li ₂ O, Li ₂ CO _3, or the like. The coating may reduce the reliability and performance of the battery. The film thus formed acts as a resistive layer,

You can neglect the growth of dendrites.

Hereinafter, the positive electrode and the separator of the lithium secondary battery except for the above-described negative electrode will be described schematically. The positive electrode according to the embodiment of the present invention includes a current collector and a positive electrode active material layer formed on the current collector.

As the positive electrode active material, a reversible intercalation and deintercalation ⁰ compound (lithiated intercalation compound) of lithium can be used. Specifically, it may include at least one selected from the group consisting of aluminum, cobalt, manganese, nickel, and combinations thereof.

 The positive electrode active material layer may further include at least one of a binder and a conductive material.

 The binder adheres positively to the positive electrode active material particles, and also adheres the positive electrode active material to the current collector, for example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride Carboxylated polyvinylchloride

Polyvinyl fluoride, polymer including ethylene oxide,

Polyvinylpyridone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like, including but not limited to no.

 The conductive material is used to impart conductivity to the positive electrode, and any battery can be used as long as it is an electronic conductive material without causing chemical change in the battery, and for example, natural graphite, artificial graphite, carbon black, acetylene black, and ketjen. Metal powders, such as black, carbon fiber, copper, nickel, aluminum, silver, metal fiber, etc. can be used, and conductive materials, such as a polyphenylene derivative, can be used 1 type or in mixture of 1 or more types.

 The negative electrode and the positive electrode are prepared by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and applying the composition to a current collector. Since such an electrode manufacturing method is well known in the art, detailed description thereof will be omitted. N-methylpyridone may be used as the solvent, but is not limited thereto.

Depending on the type of lithium secondary battery, a separator may be positioned between the positive electrode and the negative electrode. As the separator, polyethylene, polypropylene, polyvinylidene fluoride or two or more multilayer films thereof may be used.

Mixed multilayer membranes such as polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator, etc. may be used.

 In addition, the electrolyte solution that can be used in the present invention is a salt having a structure such as A + B-, A + includes an ion consisting of an alkali metal cation such as Li +, Na +, K + or a combination thereof, Β- is PF6-, BF4 -Salts containing ions consisting of anions such as C1-, Br-, I-, C104- AsF6-, CH3C02-, CF3S03-, N (CF3S02) 2-, C (CF2S02) 3- or combinations thereof Propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethecethane, diethoxyethane, tetrahydro Dissolved or dissociated in an organic solvent consisting of furan, N-methyl-2-pyridone (NMP), ethylmethylcarbonate (EMC), gamma-butyrolactone (γ-butyrolactone) or a combination thereof However, the present invention is not limited thereto.

 [Form for implementation of invention]

 Hereinafter, look at the performance of the battery according to the present invention through Comparative Example 1 and Examples 1 to 8. Comparative Example 1

 A 20 um thick copper current collector was used as the substrate. 1.7 g

After charging lithium (Honzo metal, Japan) on a molybdenum boat, 10 μm thick lithium was uniformly deposited on a copper current collector on a copper current collector by vacuum thermal evaporation.

The initial vacuum was maintained at 7 x 10 ^"7 torr or less, and the deposition pressure was 6 to 8 x 10 ^'6 torr. The deposition rate of lithium was kept constant at 3 nm / sec, and the uniformity of the lithium thin film was improved. The substrate was rotated at 4 rpm to allow the process to proceed in a dry room where the dew point was maintained below -45 ° C, and then ventilated using the atmosphere in the dry room. Lithium was prepared. Example 1 ex-si tu LiF thin film coating 16nm

 Lithium fluoride (LiF), which is one of lithium halides, was coated on the lithium thin film of lOum formed in Comparative Example 1. The initial vacuum degree for depositing lithium fluoride (TASCO, 3N, 3-6 Pa) was the same as that of the deposition of a lithium thin film, and a 16 nm LiF coating layer was deposited at a deposition rate of 3 nm / min. Except for this, it is the same as Comparative Example 1. Example 2: ex-si tu LiF thin film coating 50nm

 Under the same conditions as in Example 1, on the lithium thin film,

Lithium fluoride was deposited. Example 3: ex-si tu LiF thin film coating 80nm

 Under the same conditions as in Example 1, an 80 nm LiF coating layer was deposited on the Li thin film. Example 4: in-situ LiF thin film coating 16 nm

 Under the same conditions as in Example 1, after depositing a lithium thin film of 100 μm on a copper substrate, lithium fluoride was immediately deposited to a thickness of 16 nra while maintaining a vacuum. Example 5: in-situ LiF thin film coating 50 nm

 Under the same conditions as in Example 4, 50 nm of lithium fluoride was deposited on a lithium thin film of 100 μm. Example 6: in-situ LiF thin film coating 80nm

Under the same test conditions as in Example 4, 80 nm of lithium fluoride was deposited on a 100 μm lithium thin film. Comparative Example 1 and Examples 1 to 6 described above are summarized in Table 1 below.

 Table 1

코인셀 제조 및 전기화학성능 평가

Coin Cell Manufacturing and Electrochemical Performance Evaluation

 Coin cells were prepared using the lithium thin films for Comparative Examples 1 and 1 to 6, and the electrochemical performance was evaluated. The anode was made of Coin 2032, and the anode was made of 14 mm diameter lithium thin film deposited on a copper current collector.

The negative electrode was punched out with a diameter of 16 kPa lithium foil (Honjo) of 500 urn thickness. Asymmetric Cel 1 was prepared by placing a separator made of PP (po lypropyl ene, 25um, ce lgard) between the anode and the cathode. As electrolyte, 1M LiPF ₆ (Solbrain) was dissolved in EC: EMC = 3: 7 (v / v) and no additive was used.

 On the other hand, before evaluating electrochemical performance before and after coating film application, it was examined whether the deposited lithium thin film can be used as a cathode. Specifically, the capacity expression rate (%) was measured by stripping all of the lithium thin films at a relatively low current density. The capacity expression rate was measured before and after the deposition of the lithium thin film deposited to a thickness of 100 μm. The weight of lithium deposited from the difference was calculated. From this, the theoretical capacity (Qo) was calculated and the actual capacity () was measured from the full stripping test.

As shown in FIG. 3, the voltage test result for capacity was theoretically calculated to have a capacity of 1.931 mAh / cm ² from the thickness of the deposited lithium film. Actual measured value was 1.929mAh / cm ^{2 It} was confirmed that the capacity expression rate is 99.9%. At this time, a constant current of 0.166 mA / cm ² was applied, and the measurement was terminated when the voltage reached IV.

Then, to evaluate the electrochemical performance, a layer / discharge (Toyo) experiment was conducted at a current density of ImA / cm ² , and the layer / discharge time was 60 minutes, and the total layer / discharge depths were ImAh / cm ^2, respectively. The breakdown voltage was set to + 1V and -IV.

 4 to 10 are graphs of the results of layer discharge / discharge tests of the lithium thin film according to Comparative Example 1 and Examples 1 to 6, respectively. The layer / discharge depth criterion is a condition in which lithium having a thickness of about 5 μm is layered on the surface of a lithium thin film and discharged again during initial layer discharge.

 Up to the first 10 cycles, Comparative Example 1 and Examples 1 to 6 all show similar voltage curves (vol tage prof i le) without a significant increase in resistance, and it can be seen that the layer / discharge is smoothly performed.

 On the other hand, after 10 cycles, there is no significant resistance change during layer deposition on the basis of the lithium thin film (anode) of lOum, but it can be seen that the voltage increases rapidly at the termination stage during discharge. Existing lithium during discharge through layer discharge / discharge

Lithium is stripped from the thin film, and it appears that the resistance suddenly increases due to the rapid change of the specific surface area due to the non-uniform stripping and the rapid growth of the thin film between the negative electrode and the electrolyte.

 14 cycles of cycle life compared to Comparative Example 1

This means that the mobility of lithium ions from the uniformly coated protective film is improved. In particular, Example 6 confirmed that the cycle life is improved up to 17 times. The cycle life according to Comparative Example 1 and Examples 1 to 6 is summarized in Table 2 below.

 Table 2

 Downtime Cycle

Comparative Example 1 21 h 10.5

Example 1 24 hours 12

Example 2 26 h 13

Example 3 28 h 14 Example 4 26 h 13

Example 5 29 h 14.5

Example 6 34 hours 17 FIG. 11 is Comparative Example 1, FIG. 12 is Example 3 coated with LiF ex-situ at an 80 占 thickness on top of LiOum, and FIG. 13 is coated with in-si tu. ESCA depth profile measurement results for 6. The measuring equipment is ESCA LAB250 of VG scient if ic. For elemental analysis, X-ray was analyzed by irradiating monochromatic Al 15kV 15mA to the area of about 1.1 隱² , and ion gun was 3kV for depth profile. the Ar ⁺ ions were sputtered by irradiating the 3匪² region. At this time, the sputtering rate was based on Ta ₂ 0 ₅ 3.6 nm / min.

According to the ESCA depth profile measurement result, Comparative Example 1 confirmed that the C and 0, etc. are located in the surface portion. This may be due to Li ₂ CO ₃ , LiOH, due to atmospheric exposure after lithium deposition, and Li ₂ 0 is present in the lower part.

Confirmed. In the case of Comparative Example 1 it was confirmed that the pure lithium is located while decreasing in the depth direction.

Looking at Example 3 with reference to Figure 12, it can be confirmed that the LiF is coated by the F is detected on the surface portion, the Li ₂ 0 is present in the lower LiF coated surface as 0 is rapidly increased in the portion where F is missing. And it was found.

 On the other hand, according to Example 6 shown in FIG. 13, when F was coated with in-si tu, F was largely detected at the surface portion, and it was confirmed that oxygen was hardly detected at a position decreasing in the depth direction. That is, it was confirmed that the Li electrode directly in contact with the LiF layer is located.

 While specific embodiments of the present invention have been described and illustrated above, it is to be understood that the present invention is not limited to the described embodiments, and that various modifications and changes can be made without departing from the spirit and scope of the invention. It is self-evident to those who have. Therefore, such modifications or variations are separately from the technical spirit or aspect of the present invention.

It should not be understood that the modified embodiments should belong to the claims of the present invention.

Claims

[Claim]  [Claim 1]  Coating a negative electrode active material on a current collector to form a negative electrode active material layer, and coating a protective film on the negative electrode active material layer; Coating the protective film is a method of manufacturing a negative electrode for a lithium secondary battery using a thermal evaporation process.  [Claim 2]  In paragraph 1, The protective film is a method of manufacturing a negative electrode for a lithium secondary battery is formed to a thickness of about 10 nm to about 500 nm.  [Claim 3]  In paragraph 1, At least one of the step of forming the negative electrode active material layer and the step of forming the protective film is a method of manufacturing a negative electrode for a lithium secondary battery is carried out in a vacuum.  [Claim 4]  In paragraph 3, Forming the protective film is a method of manufacturing a negative electrode for a lithium secondary battery is performed by opening the chamber.  [Claim 5]  In paragraph 1, The current collector is at least one selected from the group consisting of copper, gold, nickel and alloys thereof.  [Claim 6]  In paragraph 1, The negative electrode active material is at least one selected from the group consisting of lithium, lithium alloy, and carbon material manufacturing method of a negative electrode for a lithium secondary battery.  [Claim 7]  In paragraph 1, The protective film is a method for producing a negative electrode for a lithium secondary battery is a lithium halide. [Claim 8]  In the U port The negative electrode active material layer is formed using a crab 1 boat, the protective film is formed using a second boat, the partition wall o is located between the first boat and the second boat is a manufacturing method of a negative electrode for a lithium secondary battery.  [Claim 9]  In paragraph 1, The negative electrode active material layer is a method of manufacturing a negative electrode for a lithium secondary battery in direct contact with the protective film.  [Claim 10]  The negative electrode for a lithium secondary battery formed using the manufacturing method of the negative electrode for lithium secondary batteries in any one of Claims U-9.  [Claim 11]  anode, Cathode, and A separator located between the anode and the cathode; The negative electrode is a lithium secondary battery formed using the method of manufacturing a negative electrode for any one of the lithium secondary battery of claim 1.