KR102639661B1 - Lithium Secondary Battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery manufactured as a negative electrode-free battery and forming lithium metal on the negative electrode by charging. The lithium secondary battery forms lithium metal in a state blocked from the atmosphere, so that the surface oxide film (native layer) formed on the conventional negative electrode does not naturally occur, thereby preventing a decrease in the efficiency and lifespan characteristics of the battery. there is. In addition, the lithium secondary battery has a three-dimensional structure in which a separate active material layer is not formed, and a metal is formed on one side of the negative electrode. Due to the potential difference between both sides of the negative electrode, lithium ions move to the metal on one side of the negative electrode, forming lithium dendrites. It can inhibit growth.

Description

Lithium Secondary Battery

The present invention relates to a lithium secondary battery with an anode-free structure using a three-dimensional anode with pores.

Recently, various devices that require batteries have been developed, ranging from mobile phones, wireless home appliances, and electric vehicles, and with the development of these devices, demand for secondary batteries is also increasing. In particular, along with the trend toward miniaturization of electronic products, secondary batteries are also becoming lighter and smaller.

In line with this trend, lithium secondary batteries that use lithium metal as an active material have recently been in the spotlight. Lithium metal has the characteristics of low redox potential (-3.045 V relative to a standard hydrogen electrode) and high weight energy density (3,860 mAhg ^-1 ), so it is expected to be a negative electrode material for high-capacity secondary batteries.

However, when lithium metal is used as a battery negative electrode, the battery is generally manufactured by attaching lithium foil to a flat current collector. Since lithium is an alkali metal and is highly reactive, it reacts explosively with water and also reacts with oxygen in the atmosphere. It has the disadvantage of being difficult to manufacture and use in a general environment. In particular, when lithium metal is exposed to the atmosphere, it forms oxide films such as LiOH, Li ₂ O, and Li ₂ CO ₃ as a result of oxidation. When a surface oxide film (native layer) is present on the surface, the oxide film acts as an insulating film, lowering electrical conductivity, and impeding the smooth movement of lithium ions, resulting in increased electrical resistance.

For this reason, the problem of surface oxide film formation due to the reactivity of lithium metal has been partially improved by performing a vacuum deposition process to form the lithium cathode, but it is still exposed to the atmosphere during the battery assembly process, and it is impossible to fundamentally suppress the formation of the surface oxide film. am. Accordingly, there is a need for the development of a lithium metal electrode that can solve the problem of lithium's reactivity and simplify the process while increasing energy efficiency by using lithium metal.

For this reason, the problem of surface oxide film formation due to the reactivity of lithium metal has been partially improved by performing a vacuum deposition process to form the lithium cathode, but it is still exposed to the atmosphere during the battery assembly process, and it is impossible to fundamentally suppress the formation of the surface oxide film. am. Accordingly, there is a need for the development of a lithium metal electrode that can solve the problem of lithium's reactivity and simplify the process while increasing energy efficiency by using lithium metal.

Korean Patent Publication No. 2016-0138120 (2016.12.02)

In order to solve the above problem, the present inventors conducted research from various angles and found that the lithium ions transferred from the positive electrode active material through charging after battery assembly can be fundamentally blocked from contact of lithium metal with the atmosphere during battery assembly. An anode-free battery structure capable of forming lithium metal was designed, and a three-dimensional anode structure capable of stably forming the lithium metal was developed.

Accordingly, the purpose of the present invention is to provide a lithium secondary battery with improved performance and lifespan by solving problems caused by the reactivity of lithium metal and problems occurring during the assembly process.

In order to achieve the above object, the present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between them, and an electrolyte, wherein the negative electrode includes a metal formed on the lower surface located opposite to the upper surface facing the separator, Provided is a lithium secondary battery, which has a three-dimensional structure with pores and in which lithium ions are moved from the positive electrode by charging to form lithium metal on the negative electrode.

At this time, the lithium metal is formed through one-time charging at a voltage of 4.5 V to 2.5 V.

The lithium secondary battery according to the present invention is coated in a state blocked from the atmosphere through the process of forming lithium metal on the negative electrode, thus suppressing the formation of a surface oxide film due to oxygen and moisture in the atmosphere of lithium metal, resulting in This has the effect of improving cycle life characteristics.

In addition, according to the present invention, in the three-dimensional structure cathode with pores, the seed metal deposited on the lower surface located opposite to the upper surface facing the separator causes the lower surface to have a lower reduction potential than the upper surface. Due to the potential difference between the upper and lower surfaces of the three-dimensional structure negative electrode formed accordingly, lithium ions move to the lower surface of the negative electrode, thereby preventing the growth of lithium dendrites.

In addition, as the growth of lithium dendrites is prevented in the three-dimensional structure negative electrode according to the present invention, battery performance such as cycle life can be improved when the three-dimensional structure negative electrode is applied to a lithium secondary battery.

1 is a schematic diagram of a lithium secondary battery manufactured according to a first embodiment of the present invention.
Figure 2 is a schematic diagram showing the movement of lithium ions (Li ⁺ ) during initial charging of a lithium secondary battery manufactured according to the first embodiment of the present invention.
Figure 3 is a schematic diagram after initial charging of a lithium secondary battery manufactured according to the first embodiment of the present invention is completed.
Figure 4 is a schematic diagram of a lithium secondary battery manufactured according to a second embodiment of the present invention.
Figure 5 is a schematic diagram showing the movement of lithium ions (Li ⁺ ) during initial charging of a lithium secondary battery manufactured according to the second embodiment of the present invention.
Figure 6 is a schematic diagram after initial charging of a lithium secondary battery manufactured according to the second embodiment of the present invention is completed.
Figure 7 shows a schematic diagram of the cathode according to the present invention.

Hereinafter, the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to this specification.

In the drawings, parts unrelated to the description are omitted in order to clearly explain the present invention, and similar reference numerals are used for similar parts throughout the specification. Additionally, the sizes and relative sizes of components shown in the drawings are unrelated to actual scale and may be reduced or exaggerated for clarity of explanation.

The top of the three-dimensional structure cathode used in this specification refers to one side of the three-dimensional structure cathode and the side facing the separator.

The bottom of the three-dimensional structure cathode used in this specification refers to the other side of the three-dimensional structure cathode, and refers to the side facing the separator, that is, the opposite side of the top surface.

The term “anode free battery” used in the present invention generally refers to a lithium secondary battery including a negative electrode in a form in which the negative electrode mixture contained in the negative electrode is formed by charging and discharging the battery. At this time, anode has the same meaning as a negative electrode.

That is, in the present invention, a negative electrode-free battery may be a negative electrode-free battery in which a negative electrode is not formed on the negative electrode current collector upon initial assembly, and a negative electrode may be formed on the negative electrode current collector depending on use. It may be a concept that includes all batteries that can be used.

In addition, in the negative electrode of the present invention, the form of the lithium metal formed as a negative electrode mixture on the negative electrode current collector includes a form in which the lithium metal is formed in a layer, and a structure in which the lithium metal is not formed in a layer (for example, a structure in which the lithium metal is not formed in a layer) Includes all structures (structures aggregated in the form of particles).

Hereinafter, the present invention will be described based on the form of the lithium metal layer formed in layers of lithium metal, but it is clear that this description does not exclude structures in which lithium metal is not formed in layers.

1 is a cross-sectional view of a lithium secondary battery manufactured according to a first embodiment of the present invention, including a positive electrode 10 including a positive electrode current collector 11 and a positive electrode mixture 12; A cathode 20 including a metal 23 formed on a lower surface 22 located on the opposite side of the upper surface 21 facing the separator 30 and having a three-dimensional structure with pores; and a separator 30 and an electrolyte (not shown) interposed between them.

The negative electrode of a lithium secondary battery is usually formed on a negative electrode current collector, but in the present invention, it includes a metal 23 formed on the lower surface 22 located on the opposite side of the upper surface 21 facing the separator 30. After assembling a negative electrode-free battery structure using a negative electrode 20 having a three-dimensional structure with pores, lithium ions released from the positive electrode mixture 12 by charging are deposited on the negative electrode 20 as lithium metal as a negative electrode mixture. By forming (not shown), a negative electrode having a composition of a known negative electrode current collector/negative electrode mixture is formed, forming a typical lithium secondary battery.

Figure 2 is a schematic diagram showing the movement of lithium ions (Li ^{+ ) during initial charging of a lithium secondary battery manufactured according to the first embodiment of the present invention, and Figure 3 is a schematic diagram showing the movement of lithium ions (Li +} ) manufactured according to the first embodiment of the present invention. This is a schematic diagram after the initial charging of the secondary battery is completed.

2 and 3, when charging is performed by applying a voltage above a certain level to a lithium secondary battery having a negative electrode-free battery structure, lithium ions are desorbed from the positive electrode mixture 12 in the positive electrode 10, This passes through the separator 30 and moves toward the cathode 20, and forms lithium metal 24 made purely of lithium on the cathode 20 to form the cathode 20. In particular, the use of metal particles made of a metal or metalloid that can form an alloy with lithium makes it easier to form the lithium metal 24 and forms a more dense thin film structure.

The formation of lithium metal 24 through this charging can form a thin film layer compared to the conventional cathode that sputters lithium metal 24 on the cathode 20 or combines lithium foil and the cathode 20. , there is an advantage that it is very easy to control the interface properties. In addition, since the bonding strength of the lithium metal 24 stacked on the cathode 20 is large and stable, the problem of being removed from the cathode 20 due to ionization again through discharge does not occur.

In particular, by forming a negative electrode-free battery structure, lithium metal is not exposed to the atmosphere at all during the battery assembly process, eliminating problems such as the formation of an oxide film on the surface due to the high reactivity of conventional lithium itself and the resulting decrease in the lifespan of lithium secondary batteries. It can be blocked fundamentally.

Meanwhile, in the lithium secondary battery according to the second embodiment of the present invention, a protective film 55 may be additionally formed on the side of the negative electrode that is in contact with the separator 60. Specifically, a protective film 55 may be formed on the negative electrode current collector 51 of the negative electrode on the surface in contact with the separator 60.

In this way, when forming the protective film 55, the lithium metal 23 is formed on the cathode 50 by passing the lithium ions transferred from the positive electrode mixture 43 through the protective film 55, as shown in FIGS. 4 and 5. form

Accordingly, the protective film 55 can be made of any material that can facilitate the transfer of lithium ions, and can be made of materials used in lithium ion conductive polymers and/or inorganic solid electrolytes, and can further contain lithium salts if necessary. there is.

Lithium ion conductive polymers, such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoride. Propylene (PVDF-HFP), LiPON, Li ₃ N, LixLa _{1 -x} TiO ₃ (0 < x < 1) and Li ₂ S-GeS-Ga ₂ S ₃ or any two of them. It may be made of the above mixture, but is not limited to this, and any polymer with lithium ion conductivity can be used without limitation.

To form the protective film 55 using a lithium ion conductive polymer, a coating solution is prepared by dissolving or swelling the lithium ion conductive polymer in a solvent and then applying it to the cathode 51.

The method of applying to the cathode 51 can be selected from known methods or a new appropriate method taking into account the characteristics of the material, etc. For example, it is desirable to distribute the polymer protective layer composition on the current collector and then uniformly disperse it using a doctor blade or the like. In some cases, a method of executing the distribution and dispersion process as a single process may be used. In addition, dip coating, gravure coating, slit die coating, spin coating, comma coating, bar coating, and reverse roll coating. It can be manufactured by performing reverse roll coating, screen coating, cap coating methods, etc. At this time, the negative electrode current collector 51 is the same as described above.

Afterwards, a drying process may be performed on the protective film 55 formed on the cathode 51. In this case, the drying process may be performed by heat treatment at a temperature of 80 to 120° C. or hot air depending on the type of solvent used in the lithium ion conductive polymer. It can be carried out by methods such as drying.

The solvent applied at this time has a solubility index similar to that of the lithium ion conductive polymer and preferably has a low boiling point. This is because mixing can be done uniformly and the solvent can be easily removed afterwards. Specifically, N,N'-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetone ( acetone), tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), Cyclohexane, water, or mixtures thereof can be used as a solvent.

When using the lithium ion conductive polymer, in order to further increase lithium ion conductivity, materials used for this purpose may be further included.

For example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiSCN, LiC(CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenyl borate, lithium imide It may further include lithium salts such as the like.

The inorganic solid electrolyte is a ceramic-based material, and crystalline or amorphous materials can be used, including Thio-LISICON (Li _{3 . 25} Ge _{0 .25} P _{0. 75} S ₄ ), Li ₂ S-SiS ₂ , LiI- Li ₂ S-SiS ₂ , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ , Li ₃ PS ₄ , Li ₇ P ₃ S ₁₁ , Li ₂ OB ₂ O ₃ , Li ₂ OB ₂ O ₃ -P ₂ O ₅ , Li ₂ OV ₂ O ₅ -SiO ₂ , Li ₂ OB ₂ O ₃ , Li ₃ PO ₄ , Li ₂ O -Li ₂ WO ₄ -B ₂ O ₃ , LiPON, LiBON, Li ₂ O-SiO ₂ , LiI, Li ₃ N, Li ₅ La ₃ Ta ₂ O12, Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li ₃ PO _(4-3/2w) Nw (w is w<1), Li _{3 .} Inorganic solid electrolytes such as _{6 Si 0.6} P _0.4 O ₄ are possible _. At this time, when using an inorganic solid electrolyte, lithium salt may be further included if necessary.

The inorganic solid electrolyte can be mixed with known materials such as binders and applied in the form of a thick film through slurry coating. Additionally, if necessary, it can be applied in the form of a thin film through a deposition process such as sputtering. The slurry coating method used can be appropriately selected based on the contents of the coating method, drying method, and solvent as mentioned in the lithium ion conductive polymer.

The protective film 55 containing the lithium ion conductive polymer and/or inorganic solid electrolyte as described above facilitates the formation of the lithium metal 51 by increasing the lithium ion transfer rate and at the same time forms the lithium metal 51/cathode ( When 50) is used as a cathode, the effect of suppressing or preventing the formation of lithium dendrites that occurs can be simultaneously secured.

In order to ensure the above effect, it is necessary to limit the thickness of the protective film 55.

The lower the thickness of the protective film 55, the more advantageous it is for the output characteristics of the battery, but only when it is formed at a certain thickness or more can the side reaction between lithium and the electrolyte formed on the negative electrode current collector 51 be suppressed, and further dendrite growth. can be effectively blocked. In the present invention, the thickness of the protective film 55 may preferably be 10 nm to 50 μm, more preferably 100 nm to 50 μm, and most preferably 1 μm to 50 μm. If the thickness of the protective film 55 is less than the above range, it is not possible to effectively suppress the side reaction and exothermic reaction between lithium and the electrolyte, which increases under conditions such as overcharging or high temperature storage, and thus safety cannot be improved, and if it exceeds the above range, the lithium In the case of ion conductive polymers, a long time is required for the composition of the protective film 55 to be impregnated or swollen with an electrolyte solution, and the movement of lithium ions is reduced, which may lead to a decrease in overall battery performance.

The lithium secondary battery of the second embodiment follows the contents mentioned in the first embodiment with respect to the remaining configuration except for the protective film 55.

The negative electrode according to the present invention includes a metal formed on the lower surface located opposite to the upper surface facing the separator, has pores formed and has a three-dimensional structure, and also serves as a negative electrode current collector when applied to a lithium-free secondary battery. You can do it at the same time.

Figure 7 shows a schematic diagram of the cathode according to the present invention.

Referring to FIG. 7, the cathode 20 has a three-dimensional structure with pores and includes two sides, that is, an upper surface 21 and a lower surface 22, and a metal 23 can be formed on the lower surface 22. there is. At this time, as defined above, the upper surface 21 and the lower surface 22 are divided depending on whether the cathode 20 faces the separator 30 when applied to the battery.

Since the metal 23 is formed only on the lower surface 22 of the three-dimensional structure current collector 20, and when Li is reduced and generated in the metal 23 than in the current collector during nuclear growth, less energy is required to generate Li in the metal 23. This is reduced first, and at this time, a potential difference is generated between the Li (Li standard, 0V) generated on the lower surface and the upper surface (3V). By the potential difference between the upper surface (21) and the lower surface (22), lithium ions form a three-dimensional structure current collector. Since it moves to the lower surface 22 of (20), the metal 23 can be said to be a seed metal that induces the movement and growth of lithium ions.

The metal 23 may be in the form of metal particles deposited on the lower surface 22 of the cathode 20.

The metal 23 is a metal that has a smaller overvoltage with the electrode active material compared to the electrode current collector; Alternatively, it may be a metal having an electrode active material and a multiphase phase.

For example, when the electrode active material is lithium metal, a metal with a smaller overvoltage compared to Cu (current collector) when forming lithium metal is a metal with low interfacial energy when reacting with lithium metal, or the size of the diffusion energy barrier of Li ions on the metal surface is small. As a metal equivalent to or lower than Li, it may be one or more types selected from the group consisting of Au, Zn, Mg, Ag, Al, Pt, In, Co, Ni, Mn, and Si, and may be in a multiphase phase with the lithium metal. ) The metal having a plurality of sites capable of reacting with lithium metal may be Ca, but is not limited thereto. Preferably, the metal 13 may be Au.

The metal 23 may be included in an appropriate amount based on the total weight of the cathode 20 on which the metal 23 is formed. If the content of the metal 23 is excessively small, the potential difference of the cathode 20 cannot be induced, so the effect of inhibiting lithium dendrite growth due to lithium ion movement is minimal, and if the content of the metal 23 is excessively large, the metal 23 ), the pores of the cathode 20 are blocked, making it difficult to use one side of the cathode 20, so it may not be possible to take advantage of the three-dimensional structure of the cathode with pores.

In the present invention, the porosity of the cathode 20 may be 50 to 90%, preferably 60 to 80%, and more preferably 65 to 75%. If the porosity is less than the above range, the effect of inhibiting lithium dendrite growth in a lithium secondary battery using the anode 20 is minimal, and if it exceeds the above range, the mechanical properties of the anode 20 may be reduced.

In the present invention, the thickness of the cathode 20 may be 20 to 200 ㎛, preferably 50 to 150 ㎛, and more preferably 80 to 120 ㎛. If the thickness of the anode 20 is less than the above range, the durability of the anode 20 may decrease, and if it exceeds the above range, the battery may become thick.

In the present invention, the cathode 20 may be made of an electrically conductive metal, and the electrically conductive metal may be at least one selected from the group consisting of Al, Cu, Au, Ag, In, Mg, Ni, and alloys thereof. You can. Depending on the redox potential of the metal, it can be used as a positive electrode current collector or a negative electrode current collector. Preferably, the cathode 20 may be made of Cu.

The method of manufacturing a cathode as described above may include forming a metal on one surface of a three-dimensional cathode.

The metal may be formed on one surface of the cathode by deposition, specifically thermal evaporation, e-beam evaporation, chemical vapor deposition (CVD), and physical vapor deposition. It can be formed by a deposition method selected from the group consisting of (PVD) method.

The implementation of a lithium secondary battery with a negative electrode-free structure, which includes a metal formed on the lower surface located on the opposite side of the upper surface facing the separator and has a negative electrode 20 with a three-dimensional structure with pores, can be implemented in various ways. , In the present invention, this is secured by controlling the composition used in the positive electrode mixture 12.

The positive electrode mixture 12 can use a variety of positive electrode active materials depending on the type of battery. The positive active material used in the present invention is not particularly limited as long as it is a material that can occlude and release lithium ions, but has current life characteristics and charge. Lithium transition metal oxide is typically used as a positive electrode active material that can produce batteries with excellent discharge efficiency.

Lithium transition metal oxides include layered compounds containing two or more transition metals, such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ) substituted with one or more transition metals; Lithium manganese oxide substituted with one or more transition metals, lithium nickel-based oxide, spinel-based lithium nickel manganese composite oxide, spinel-based lithium manganese oxide in which part of Li in the chemical formula is substituted with an alkaline earth metal ion, olivine-based lithium metal phosphate, etc. However, it is not limited to these alone.

It is preferable to use lithium-containing transition metal oxides, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c )O ₂ (0＜a＜1, 0＜b ＜1, 0＜c＜1, a+b+c=1), LiNi _1-Y Co _Y O ₂ , LiCo _{1 - Y} MnYO ₂ , LiNi _{1 - Y} MnYO ₂ (where 0=Y＜1) , Li(NiaCobMnc)O4(0＜a＜2, 0＜b＜2, 0＜c＜2, a+b+c=2), LiMn _{2 - z} Ni _z O4, LiMn _{2 - z} Co _z O ₄ ( _where 0 _＜ Z＜ _{2 )} , _Li , Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi, A is -1 or -2 valent one or more anions), Li _{1 + a} NibM' _{1- b} O _{2 -c} A' _c (0≤a≤0.1, 0≤b≤0.8, 0≤c<0.2, M' is Mn, Co, Mg, At least one selected from the group consisting of stable elements of 6 coordination, such as Al, and A' is one or more anions of -1 or -2 valence.), LiCoPO ₄ , and LiFePO ₄ . It is possible, preferably LiCoO ₂ is used. Additionally, in addition to these oxides, sulfide, selenide, and halide can also be used.

Additionally, in the present invention, a lithium metal compound can be used as an additive that can provide a lithium source to lithium transition metal oxide.

The lithium metal compound presented in the present invention can be a compound represented by the following formulas 1 to 8.

[Formula 1]

Li ₂ Ni _1-a M ¹ _a O ₂

(In the above formula, a is 0≤a<1, and M ¹ is one or more elements selected from the group consisting of Mn, Fe, Co, Cu, Zn, Mg, and Cd.)

[Formula 2]

Li _2+b Ni _1-c M ² _c O _2+d

(In the above formula, -0.5≤b<0.5, 0≤c≤1, 0≤d<0.3, M ² is P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, It is one or more elements selected from the group consisting of Cu, Zn, Cr, Mg, Nb, Mo, and Cd.)

[Formula 3]

LiM ³ _e Mn _{1 - e} O ₂ (x is 0≤e<0.5, and M ³ is one or more elements selected from the group consisting of Cr, Al, Ni, Mn, and Co.),

[Formula 4]

Li ₂ M ⁴ O ₂

(In the above formula, M ⁴ is one or more elements selected from the group consisting of Cu and Ni.)

[Formula 5]

Li _3+f Nb _1-g M ⁵ _g S _4-h

(In the above formula, -0.1≤f≤1, 0≤g≤0.5, -0.1≤h≤0.5, and M ⁵ is one or more elements selected from the group consisting of Mn, Fe, Co, Cu, Zn, Mg, and Cd. am)

[Formula 6]

LiM ⁶ _i Mn _1-i O ₂

(In the above formula, i is 0.05≤x<0.5, and M ⁶ is one or more elements selected from the group consisting of Cr, Al, Ni, Mn, and Co.)

[Formula 7]

LiM ⁷ _2j Mn _2-2j O ₄

(In the above formula, j is 0.05≤x<0.5, and M ⁷ is one or more elements selected from the group consisting of Cr, Al, Ni, Mn, and Co.)

[Formula 8]

Li _k -M ⁸ _m -N _n

(In the above formula, M ⁸ represents an alkaline earth metal, k/(k+m+n) is 0.10 to 0.40, m/(k+m+n) is 0.20 to 0.50, and n/(k+m+ n) is 0.20 to 0.50.)

The lithium metal compounds of Formulas 1 to 8 have different irreversible capacities depending on their structures. They can be used alone or in combination, and serve to increase the irreversible capacity of the positive electrode active material.

For example, highly irreversible substances represented by Formulas 1 and 3 have different irreversible capacities depending on their type, and have values as shown in Table 1 below.

Initial charge capacity (mAh/g) Initial discharge capacity (mAh/g) Initial Coulomb Efficiency Initial irreversible capacity ratio [Formula 1] Li ₂ NiO ₂ 370 110 29.7% 70.3% [Formula 3] LiMnO ₂ 230 100 43.5% 56.5% [Formula 3] LiCr _x Mn _1-x O ₂ 230 80 34.8% 65.2%

In addition, the lithium metal compound of Formula 2 preferably belongs to the space group Immm, and among them, Ni, M composite oxide forms planar tetra-coordinated (Ni, M)O4, and the planar tetra-coordinated structure forms opposite sides. It is more preferable that they share (sides formed by O-O) and form a primary chain. The crystal lattice constants of the compound of Formula 2 are preferably a = 3.7 ± 0.5 Å, b = 2.8 ± 0.5 Å, c = 9.2 ± 0.5 Å, α = 90°, β = 90°, γ = 90°. Additionally, the lithium metal compound of Formula 8 has an alkaline earth metal content of 30 to 45 atomic% and a nitrogen content of 30 to 45 atomic%. At this time, when the content of the alkaline earth metal and the content of nitrogen are within the above range, the thermal properties and lithium ion conduction properties of the compound of Formula 1 are excellent. And, in Formula 8, k/(k+m+n) is 0.15 to 0.35, for example, 0.2 to 0.33, and m/(k+m+n) is 0.30 to 0.45, for example, 0.31 to 0.33, n/(k+m+n) is 0.30 to 0.45, for example 0.31 to 0.33.

According to one embodiment of the electrode active material of Formula 1, a is 0.5 to 1, b is 1, and c is 1.

When a coating film is formed with any one of the compounds of Formulas 1 to 8, the electrode active material exhibits stable characteristics while maintaining low resistance characteristics even in an environment where lithium ions are continuously inserted and desorbed. In the electrode active material according to one embodiment of the present invention, the thickness of the coating film is 1 to 100 nm. When the thickness of the coating film is within the above range, the ion conduction characteristics of the positive electrode active material are excellent.

Additionally, the average particle diameter of the positive electrode active material is 1 to 30 μm, and according to one embodiment, 8 to 12 μm. When the average particle size of the positive electrode active material is within the above range, the capacity characteristics of the battery are excellent.

The core active material doped with the alkaline earth metal may include, for example, LiCoO ₂ doped with magnesium. The content of magnesium is 0.01 to 3 parts by weight based on 100 parts by weight of the core active material.

The lithium transition metal oxide described above is used as a positive electrode active material in the positive electrode mixture 12 along with a binder and a conductive material. In the anode-free battery structure of the present invention, the lithium source for forming lithium metal 24 is the lithium transition metal oxide. That is, when the lithium ions in the lithium transition metal oxide are charged within a specific voltage range, the lithium ions are desorbed to form lithium metal 24 on the cathode 20.

In the present invention, the charging range for forming lithium metal 24 is performed in a voltage range of 4.5V to 2.5V, preferably 4.0V to 3.0V, and more preferably 3.7V to 3.3V. If charging is performed below the above range, it becomes difficult to form lithium metal 24. Conversely, if charging is performed beyond the above range, damage to the cell occurs and charging and discharging proceeds properly after overdischarge occurs. It doesn't work.

The formed lithium metal 24 may form a discontinuous layer on the cathode 20. In other words, the discontinuous layer is discontinuously distributed, and there are areas where lithium metal 24 is present and areas where lithium metal 24 is not present within a specific area, and lithium compounds are present in the area where lithium metal 24 is not present. This means that the region where the lithium metal 24 exists is distributed without continuity by distributing the region in such a way that it is isolated, disconnected, or separated like an island type.

The lithium metal 24 formed through such charging and discharging may be in the form of a lithium A metal layer having a thickness of at least 50 nm or more and 100 μm or less, preferably 1 μm to 50 μm, to function as a negative electrode. If the thickness is less than the above range, the battery charging and discharging efficiency decreases rapidly. Conversely, if the thickness exceeds the above range, the lifespan characteristics are stable, but the energy density of the battery is lowered.

In particular, the lithium metal 24 presented in the present invention is manufactured as a negative electrode-free battery without lithium metal during battery assembly, so compared to a lithium secondary battery assembled using a conventional lithium foil, the lithium metal 24 generated during the assembly process is high. Due to its reactivity, no or little oxide layer is formed on the lithium metal 24. As a result, it is possible to prevent degradation of battery life caused by the oxidation layer.

Additionally, the lithium metal 24 moves by charging of a highly irreversible material, which can form a more stable lithium metal 24 compared to forming the lithium metal 24 on the anode. When lithium metal is attached to the anode, a chemical reaction between the anode and the lithium metal may occur.

A positive electrode mixture 12 is composed of the above-mentioned positive electrode active material and a lithium metal compound. At this time, the positive electrode mixture 12 may further include conductive materials, binders, and other additives commonly used in lithium secondary batteries. You can.

Conductive materials are used to further improve the conductivity of the electrode active material. These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery, and examples include graphite such as natural graphite or artificial graphite; Carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives, etc. may be used.

A binder may be further included to bond the positive electrode active material, lithium metal compound, and conductive material and to the current collector. The binder may include a thermoplastic resin or thermosetting resin. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer, vinylidene fluoride- Hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene Roethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene copolymer, ethylene -Acrylic acid copolymers, etc. can be used alone or in combination, but are not necessarily limited to these, and any binder that can be used as a binder in the relevant technical field can be used.

Examples of other additives include fillers. The filler is selectively used as a component to suppress the expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. For example, olifin-based polymers such as polyethylene and polypropylene, and fibrous materials such as glass fiber and carbon fiber are used.

The positive electrode mixture 12 of the present invention is formed on the positive electrode current collector 11.

The positive electrode current collector is generally made to have a thickness of 3 ㎛ to 500 ㎛. The positive electrode current collector 11 is not particularly limited as long as it has high conductivity without causing chemical changes in the lithium secondary battery, and examples include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. A surface treated with carbon, nickel, titanium, silver, etc. may be used. At this time, the positive electrode current collector 11 may be used in various forms such as a film, sheet, foil, net, porous material, foam, or non-woven material with fine irregularities formed on the surface to increase adhesion with the positive electrode active material.

The method of applying the positive electrode mixture 12 on the current collector includes distributing the electrode mixture slurry on the current collector and then uniformly dispersing it using a doctor blade, etc., die casting, and comma coating. Methods such as comma coating and screen printing may be mentioned. Additionally, the electrode mixture slurry may be bonded to the current collector by pressing or lamination after molding on a separate substrate, but is not limited thereto.

Meanwhile, as shown in the structures of Figures 3 and 6, the lithium secondary battery includes a positive electrode 10, a negative electrode 20, a separator 30 and an electrolyte (not shown) interposed between them, and the type of battery. Accordingly, the separator 30 may be excluded.

The separator may be made of a porous substrate, and the porous substrate may be any porous substrate commonly used in electrochemical devices. For example, a polyolefin-based porous membrane or non-woven fabric may be used. There is no particular limitation.

Examples of the polyolefin-based porous membrane include polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, each singly or a mixture thereof. One membrane can be mentioned.

The nonwoven fabric includes, in addition to polyolefin-based nonwoven fabric, for example, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, and polycarbonate. ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, respectively, individually or Examples include nonwoven fabrics formed from polymers that are a mixture of these. The structure of the nonwoven fabric may be a sponbond nonwoven fabric composed of long fibers or a melt blown nonwoven fabric.

The thickness of the porous substrate is not particularly limited, but is 1 ㎛ to 100 ㎛, or 5 ㎛ to 50 ㎛.

The size and pore size of the pores present in the porous substrate are also not particularly limited, but may be 0.001 ㎛ to 50 ㎛ and 10% to 95%, respectively.

Additionally, the electrolyte salt contained in the non-aqueous electrolyte solution that can be used in the present invention is a lithium salt. The lithium salt may be used without limitation to those commonly used in electrolytes for lithium secondary batteries. For example, the lithium salt is LiFSI, LiPF ₆ , LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, and lithium 4-phenyl borate.

Organic solvents included in the above-mentioned non-aqueous electrolyte solution can be used without limitation those commonly used in electrolyte solutions for lithium secondary batteries, for example, ether, ester, amide, linear carbonate, cyclic carbonate, etc., individually or in combination of two or more types. Can be used by mixing. Among them, representative examples may include carbonate compounds that are cyclic carbonates, linear carbonates, or slurries thereof.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, There is any one or two or more slurries selected from the group consisting of 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halogenates thereof. Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).

In addition, specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. Two or more types of slurries may be typically used, but are not limited thereto. In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high viscosity organic solvents and have a high dielectric constant, so they can better dissociate lithium salts in the electrolyte. These cyclic carbonates include dimethyl carbonate and diethyl carbonate. By mixing low-viscosity, low-dielectric constant linear carbonate in an appropriate ratio, an electrolyte solution with higher electrical conductivity can be made.

In addition, as the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a slurry of two or more of these may be used. , but is not limited to this.

In addition, esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, Any one or two or more slurries selected from the group consisting of σ-valerolactone and ε-caprolactone may be used, but the slurry is not limited thereto.

Injection of the non-aqueous electrolyte may be performed at an appropriate stage during the manufacturing process of the electrochemical device, depending on the manufacturing process and required physical properties of the final product. In other words, it can be applied before electrochemical device assembly or at the final stage of electrochemical device assembly.

The lithium secondary battery according to the present invention is capable of lamination (stack) and folding processes of separators and electrodes in addition to the general winding process.

Additionally, the shape of the battery case is not particularly limited, and may be of various shapes such as cylindrical, stacked, prismatic, pouch-shaped, or coin-shaped.

The present invention also provides a battery module including the lithium secondary battery as a unit cell.

The battery module can be used as a power source for medium to large-sized devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium-to-large devices include power tools that are powered by an omni-electric motor; Electric vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; Electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf cart; Examples include, but are not limited to, power storage systems.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the attached patent claims.

In the following examples, comparative examples, and experimental examples, a negative electrode having a three-dimensional structure with pores is referred to as a 3D structure negative electrode, and a current collector with a structure without pores is referred to as a 2D structure negative electrode.

Example One

(1) Manufacturing of anode

Mix LCO (LiCoO ₂ ): Super-P: Binder (PVdF) in 500 ml of acetonitrile at a weight ratio of 95:2.5:2.5, and then add L2N (Li ₂ NiO ₂ ) to it at a weight ratio of 9:1 compared to LCO. Added. Then, a slurry composition was prepared by mixing for 5 minutes with a paste face mixer.

Subsequently, the prepared slurry composition was coated on a current collector (Al Foil, thickness 15 ㎛) and dried at 50°C for 12 hours to prepare a positive electrode. At this time, the loading amount of LCO was 4.0 mAh/cm ² .

(2) Fabrication of a three-dimensional cathode and half cell with Au metal formed on the bottom surface

Au metal was thermally deposited on one side of a Cu current collector in the form of a three-dimensional foam.

(3) Manufacture of cathode-free battery

An electrode assembly is manufactured by interposing a porous polyethylene separator between the positive electrode prepared in (1) and the negative electrode in (2), the electrode assembly is placed inside the case, and electrolyte is injected to manufacture a lithium secondary battery. did. At this time, the electrolyte is 1M LiPF ₆ and 2% by weight of VC (Vinylene Carbonate) dissolved in an organic solvent consisting of EC (ethylene carbonate): DEC (diethyl carbonate): DMC (dimethyl carbonate) in a volume ratio of 1:2:1. The prepared product was used.

At this time, a lithium-free battery was manufactured by facing the bottom surface of the cathode where Au metal was formed and the separator.

Example 2

A three-dimensional cathode and a cathode-free battery were manufactured in the same manner as in Example 1, except that Ag metal was used instead of Au metal.

Example 3

A three-dimensional structure cathode and a cathode-free battery were manufactured in the same manner as in Example 1, but by reducing the amount of Au metal formed on the lower surface of the three-dimensional structure cathode.

Example 4

A three-dimensional structure cathode and a cathode-free battery were manufactured in the same manner as in Example 1, but by increasing the amount of Au metal formed on the lower surface of the three-dimensional structure cathode.

Comparative Example 1

A negative electrode-free battery was manufactured in the same manner as in Example 1, except that a Cu foil was used as a two-dimensional Cu negative electrode instead of a three-dimensional metal negative electrode.

Comparative Example 2

This was carried out in the same manner as in Example 1, except that a two-dimensional Cu cathode was used instead of a three-dimensional cathode, and a half cell was manufactured by forming Au metal on a Cu foil (product name, manufacturer).

Comparative Example 3

This was carried out in the same manner as in Example 1, except that Ag metal was formed on a Cu foil (product name, manufacturer) as a two-dimensional Cu cathode instead of a three-dimensional cathode, and then a cathode-free battery was manufactured using this.

Comparative Example 4

A negative electrode-free battery was manufactured in the same manner as in Example 1, except that no metal was formed on the Cu negative electrode in the form of a three-dimensional foam (manufacturer, product name).

Comparative Example 5

An anode-free battery was manufactured in the same manner as in Example 1, except that Au metal was formed on both sides of a three-dimensional foam-shaped Cu anode (manufacturer, product name), that is, both the upper and lower surfaces.

Comparative Example 6

An anode-free battery was manufactured in the same manner as in Example 1, except that Au metal was formed on the upper surface of a Cu anode in the form of a three-dimensional foam (manufacturer, product name).

1: Lithium secondary battery
10: anode
11: positive electrode current collector
12: Anode mixture
20, 50: cathode
21: top 22: bottom
23: metal 24: lithium metal
30: Separator
55: Shield

Claims (9)

In a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between them, and an electrolyte,
The cathode includes a metal formed on a lower surface located opposite to the upper surface facing the separator, and has a three-dimensional structure with pores,
A lithium secondary battery in which lithium ions are moved from the positive electrode by charging to form lithium metal on the negative electrode,
The cathode includes Cu,
The metal is Au particle,
A lithium secondary battery in which the metal is deposited on the lower surface of the cathode. According to paragraph 1,
A lithium secondary battery in which the lithium metal is formed through one charge in the voltage range of 4.5V to 2.5V. delete delete delete delete According to paragraph 1,
A lithium secondary battery wherein the negative electrode has a porosity of 50 to 90%. According to paragraph 1,
A lithium secondary battery wherein the anode has a thickness of 20 to 200 μm. According to paragraph 1,
A lithium secondary battery, wherein the lithium metal is a lithium metal layer having a thickness of 50 nm to 100 ㎛.