Lithium secondary battery and manufacturing method thereof

Abstract

The present invention relates to a lithium secondary battery. More specifically, the lithium secondary battery may comprise: a positive electrode including a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector; a negative electrode including a negative electrode current collector; and an electrolyte layer between the positive electrode and the negative electrode. The positive electrode active material layer contains: a positive electrode active material including first particles having a large particle diameter and second particles having a small particle diameter; and a multi-lithium additive, wherein the capacity ratio of the positive electrode active material to the multi-lithium additive evaluated by Equation 1 may be 5 / 5 to 9 / 1. [Equation 1] Capacity ratio = \{(discharge capacity per unit mass of positive electrode active material (mAh / g)) / (charge capacity per unit mass of multi-lithium additive (mAh / g))\}. In Equation 1, the charge capacity of the multi-lithium additive is defined by Equation 2. [Equation 2] Charge capacity per unit mass of multi-lithium additive (mAh / g) = [\{total charge capacity of positive electrode (mAh) – charge capacity of positive electrode active material (mAh)\} / loading amount of multi-lithium (g)].

Description

Lithium secondary battery, and method of manufacturing the same

[0001] This concerns a negative electrode lithium secondary battery.

[0002]

[0003] Currently commercially available lithium-ion batteries primarily use carbon-based negative electrode active materials, such as graphite. While carbon-based negative electrode active materials offer high battery stability due to their lack of volume change during charging and discharging, their relatively low capacity necessitates the use of high-capacity negative electrode active materials. Accordingly, lithium metal, which has a higher theoretical electrical capacity compared to carbon-based negative electrode active materials, can be used as a negative electrode active material.

[0004] However, it is difficult to use them as long-life batteries due to stability issues caused by the formation of lithium dendrites and the high reactivity of lithium metal. Therefore, development is needed to improve stability in order to use lithium metal as an anode active material.

[0005]

[0006] The problem that the present invention aims to solve is to provide a lithium secondary battery with effectively improved energy density and lifespan.

[0007] Another problem that the present invention aims to solve is to provide a method for manufacturing a lithium secondary battery with improved lifespan characteristics.

[0008]

[0009] A lithium secondary battery according to the concept of the present invention comprises: a positive electrode including a positive current collector and a positive active material layer on the positive current collector; a negative electrode including a negative current collector; and an electrolyte layer between the positive electrode and the negative electrode, wherein the positive active material layer comprises a positive active material including a first particle of large diameter and a second particle of small diameter; and a lithium additive, and the capacity ratio of the positive active material and the lithium additive evaluated by Formula 1 below may be 5 / 5 to 9 / 1.

[0010] [Equation 1]

[0011] Capacity ratio = {(Discharge capacity per unit mass of positive active material (mAh / g)) / (Charge capacity per unit mass of lithium additive (mAh / g))}

[0012] In the above Equation 1, the charging capacity of the lithium additive is defined by the following Equation 2,

[0013] [Equation 2]

[0014] Charging capacity per unit mass of lithium additive (mAh / g) = [{Total charging capacity of the anode (mAh) - Charging capacity of the anode active material (mAh)} / Loading amount of lithium additive (g)].

[0015] A lithium secondary battery according to another concept of the present invention comprises: a positive electrode including a positive current collector and a positive active material layer on the positive current collector; a negative electrode including a negative current collector and a lithium metal layer on the negative current collector; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive active material layer comprises a positive active material and a dilithium additive in a delithiated state, the average particle size of the dilithium additive is smaller than the average particle size of the positive active material, and the dilithium additive can be represented by the following chemical formula 2.

[0016] [Chemical Formula 2]

[0017] Li a2 MO b2

[0018] In the above chemical formula 2, M is an element selected from the group consisting of Ni, Co, Al, Fe, and Mo, and 1≤a2≤4, 2≤b2<4.

[0019] A method for manufacturing a lithium secondary battery according to another concept of the present invention comprises: manufacturing a positive electrode; manufacturing a negative electrode; assembling a lithium secondary battery by stacking the positive electrode and the negative electrode; and forming the lithium secondary battery, wherein the positive electrode comprises a positive active material and a lithium additive, and the negative electrode comprises a negative current collector.

[0020] Forming the lithium secondary battery comprises charging the lithium secondary battery to form a lithium metal layer on the negative current collector; and discharging the lithium secondary battery to oxidize the lithium metal layer, and after the discharge is terminated, the lithium additive may have a delithiated state.

[0021]

[0022] According to one aspect, by including a lithium additive, it is possible to provide a long-life lithium secondary battery with improved cycle characteristics by improving energy density while compensating for lithium consumption due to initial charge-discharge.

[0023]

[0024] FIG. 1 is a cross-sectional view of a lithium secondary battery according to one embodiment of the present invention.

[0025] FIG. 2 is a cross-sectional view of a lithium secondary battery according to one embodiment of the present invention.

[0026] FIG. 3 is an enlarged view of region B of FIG. 1, showing a cathode according to one embodiment of the present invention.

[0027] FIG. 4 is an enlarged view of region B of FIG. 2, showing a cathode according to one embodiment of the present invention.

[0028] FIG. 5 is an enlarged view of region A of FIG. 1, showing a positive active material layer according to one embodiment of the present invention.

[0029] FIG. 6 is an enlarged view of region A of FIG. 2, showing a positive active material layer according to one embodiment of the present invention.

[0030] FIG. 7a is an SEM image of a first particle according to one embodiment of the present invention.

[0031] FIG. 7b is an SEM image of a second particle according to one embodiment of the present invention.

[0032] FIG. 8a is an SEM image of a lithium additive according to one embodiment of the present invention.

[0033] FIG. 8b is an SEM image of a lithium additive according to one embodiment of the present invention.

[0034] FIG. 9a is an SEM image of a positive electrode active material layer according to one embodiment of the present invention.

[0035] FIG. 9b is an SEM image of a positive electrode active material layer according to one embodiment of the present invention.

[0036] FIG. 10a is an SEM image of a positive electrode active material layer according to one embodiment of the present invention.

[0037] FIG. 10b is an SEM image of a positive electrode active material layer according to one embodiment of the present invention.

[0038] The present inventive concept described below is subject to various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present inventive concept to specific embodiments and should be understood to include all modifications, equivalents, or substitutions that fall within the scope of the description of the present inventive concept.

[0039] The terms used below are used merely to describe specific embodiments and are not intended to limit the creative concept. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the following, terms such as “comprising” or “having” are intended to indicate the existence of the features, numbers, steps, actions, components, parts, components, materials, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, components, materials, or combinations thereof. As used below, “ ” may be interpreted as “and” or “or” depending on the context.

[0040] In the drawings, thicknesses have been enlarged or reduced to clearly represent various layers and regions. Throughout the specification, the same reference numerals have been used for similar parts. Throughout the specification, when a part such as a layer, film, region, or plate is described as being “on” or “above” another part, this includes not only cases where it is directly above another part but also cases where there is another part in between. Throughout the specification, terms such as “first,” “second,” etc., may be used to describe various components, but the components should not be limited by these terms. In this specification and drawings, components having substantially the same functional configuration are referred to by the same reference numerals to avoid redundant descriptions.

[0041] In the present disclosure, the “size” of a particle is, for example, the “particle diameter” of the particle. The “particle diameter” of the particle represents the average diameter when the particle is spherical and represents the average major axis length when the particle is non-spherical. The particle diameter of the particle can be measured using a particle size analyzer (PSA). The “particle diameter” of the particle is, for example, the average particle diameter. The average particle diameter is, for example, the median particle diameter (D50). The median particle diameter (D50) is the particle size corresponding to the 50% cumulative volume calculated from the side of the particle having a small particle size in the particle size distribution measured, for example by laser diffraction.

[0042] In the present disclosure, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state.

[0043] In this disclosure, “alloy” means a mixture of two or more metals.

[0044] In the present disclosure, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0045] In the present disclosure, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0046] In the present disclosure, “lithiation” and “to lithiate” refer to the process of adding lithium to a positive electrode active material or a negative electrode active material.

[0047] In the present disclosure, “delithiation” and “to delithiate” refer to the process of removing lithium from a positive electrode active material or a negative electrode active material.

[0048] In this disclosure, “charge” and “to charge” refer to the process of providing electrochemical energy to a battery.

[0049] In this disclosure, “anode” and “cathode” refer to electrodes where electrochemical reduction and lithiation occur during the discharge process.

[0050] In this disclosure, “cathode” and “anode” refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0051]

[0052] A lithium secondary battery and a method for manufacturing the same according to embodiments of the present invention will be described in detail below.

[0053] lithium secondary battery

[0054] Referring to FIG. 1, a lithium secondary battery according to one embodiment may include a positive electrode (100), a negative electrode (200), and an electrolyte layer (300). The positive electrode (100) may include a positive current collector (110) and a positive active material layer (120) on the positive current collector (110). The negative electrode (200) may include a negative current collector (210). The electrolyte layer (300) may be disposed between the positive electrode and the negative electrode. FIG. 1 shows a lithium secondary battery according to one embodiment and is a cross-sectional view of a negative electrode secondary battery immediately after assembly. On the other hand, referring to FIG. 2, it can be seen that a negative active material layer is formed on the negative current collector after the formation process of the secondary battery. A lithium secondary battery according to an embodiment of the present invention includes both a secondary battery having an initial negative electrode structure and a secondary battery including a negative electrode active material layer formed through a subsequent charge-discharge process, and can be defined as a negative electrode battery or a negative electrode secondary battery.

[0055] A cathode (200) according to one embodiment may include a cathode current collector (210). As the cathode current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used, but is not limited to materials that can be conventionally used as a cathode current collector.

[0056] FIGS. 3 and FIGS. 4 are cross-sectional views of a cathode (200) according to embodiments of the present invention. Referring to FIG. 3, the cathode (200) may have a cathode active material layer on the cathode current collector (210) omitted. That is, the cathode (200) may have an anode-free structure. Specifically, a cathode-free structure may mean that the cathode active material layer on the cathode current collector is omitted during the initial assembly stage of the lithium secondary battery. FIG. 3 may be a cross-sectional view immediately after assembly of the lithium secondary battery.

[0057] Referring to FIG. 4, a negative electrode (200) according to one embodiment may include a negative electrode active material layer (220) on a negative electrode current collector (210). The negative electrode active material layer (220) may be formed on the negative electrode current collector (210) as the charging and discharging process proceeds. This may be a cross-sectional view after the formation stage of a lithium secondary battery. That is, when manufacturing the battery, only the negative electrode current collector (210) is included as the negative electrode component, and the lithium metal formed through the charging and discharging process is used as the negative electrode active material to improve the energy density of the lithium secondary battery. Furthermore, in a lithium metal battery using high-capacity lithium metal as the negative electrode active material, the risk caused by the strong reactivity of the lithium metal can be reduced, thereby improving the stability of the manufacturing stage.

[0058] However, when lithium metal is used as the negative electrode active material, the negative electrode active material layer (220) may form dendrites depending on the growth form of the lithium metal, which may cause a short circuit. In one embodiment, a uniform lithium metal layer may be formed by providing a protective layer that physically blocks lithium dendrites or by providing a lithium host structure. In another embodiment, a negative electrode coating layer may be included to induce lithium to precipitate between the negative electrode current collector and the coating layer. The coating layer acts as a protective layer for the lithium metal and simultaneously suppresses the precipitation and growth of lithium dendrites. The negative electrode coating layer may include carbon-based particles and metal (or metalloid) particles. For example, the carbon-based particles may include at least one carbon selected from the group consisting of carbon black, acetylene black, furnace black, ketjen black, and graphene. The metal (or metalloid) particles may comprise at least one metal (or metalloid) selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn).

[0059] Furthermore, in the case of a cathode-free structure, a cathode active material layer must be formed separately through the initial charge-discharge process. Since irreversible lithium consumption—such as the formation of the lithium metal layer, reaction with the electrolyte, or the formation of the SEI (solid electrolyte layer) layer—occurs entirely through the lithium in the cathode, there is a problem of reduced actual capacity. Consequently, the realized capacity is lower than the design capacity of the cathode active material, leading to a decrease in the capacity of the lithium secondary battery. Therefore, a means is required to supply additional lithium within the battery while maintaining the advantages of lithium metal batteries through a cathode-free structure. For example, one method to prevent the reduction of reversible capacity is to adjust the charge-discharge voltage range of the lithium secondary battery; however, this may be difficult to adopt depending on the voltage range of the cathode active material. Additionally, it may be difficult to set the appropriate required capacity for the cathode based on the battery's design capacity.

[0060] Referring to FIG. 5, the cathode according to an embodiment of the present invention may further include a dilithium additive (LRA) to replenish the lithium of the cathode. The dilithium additive (LRA) may refer to a compound that contains an excess of lithium compared to a general cathode active material and can be used as a lithium source within the battery. For example, the dilithium additive may contain 2 moles or more of lithium per mole. In one embodiment, the dilithium additive may include a compound of the following chemical formula 1.

[0061] [Chemical Formula 1]

[0062] Li a1 MO b1

[0063] In the above chemical formula 1,

[0064] M is an element selected from the group consisting of Ni, Co, Al, Fe, Mo, and Cu, and 2≤a1≤6, 2≤b1≤4. For example, the lithium additive may include Li5FeO4.

[0065] In addition, the lithium additive (LRA) may include non-metallic compounds containing lithium, such as Li2O, Li3N, and Li2S.

[0066] In particular, since a secondary battery with a negative electrode structure like the present invention has a structure in which the initial negative electrode active material layer is omitted, a significantly higher irreversible capacity occurs compared to the general case, which can lead to a significant deterioration in the performance of the battery.

[0067] As described above, the darium additive may include a lithium-excess transition metal oxide containing an excess amount of lithium. The darium additive can replenish the lithium of the cathode. By including the darium additive according to one embodiment, the cathode can compensate for lithium consumption during charging and discharging. Consequently, the capacity and lifespan of the secondary battery can be improved by compensating for the irreversible loss of lithium.

[0068] The lithium additive (LRA) can serve as a lithium source for the cathode during the formation phase. During the formation phase, the lithium in the lithium additive (LRA) can be delithiated and migrate to the cathode. For example, the lithium additive (LRA) can provide lithium for forming a lithium metal layer in a cathode-free secondary battery. In addition to the cathode active material, the anode (100) contains a material containing a large amount of lithium, thereby preventing performance degradation due to irreversible lithium consumption.

[0069] By including a certain amount of lithium additive (LRA) in addition to the positive electrode active material, the energy density and lifespan characteristics of a secondary battery having a negative electrode structure can be improved.

[0070] In one embodiment, by controlling the content of the positive active material and the lithium additive (LRA) in the positive active material layer (120), the irreversible capacity of the negative electrode secondary battery can be compensated to improve the lifespan characteristics.

[0071] For example, the content of the positive active material and the lithium additive (LRA) within the positive active material layer (120) can be controlled through their respective capacity ratios. The capacity ratio of the positive active material and the lithium additive (LRA) can be calculated using the following Equation 1.

[0072] [Equation 1]

[0073] Capacity Ratio = {(Discharge capacity per unit mass of positive active material (mAh / g)) / Charge capacity per unit mass of lithium additive (mAh / g)}

[0074] In the above Equation 1, the charging capacity of the lithium additive can be defined by the following Equation 2.

[0075] [Equation 2]

[0076] Charging capacity per unit mass of lithium additive (mAh / g) = [{Total charging capacity of the cathode (mAh) - Charging capacity of the cathode active material (mAh)} / Loading amount of lithium additive (g)]

[0077] In one embodiment, the capacity ratio of the cathode active material and the lithium hydride additive evaluated as above may be in the range of 7 / 3 to 9 / 1. The capacity ratio of the cathode active material and the lithium hydride additive may be in the range of 5 / 5 to 9 / 1. If the capacity ratio is 5 / 5 or less, for example, if the charge capacity of the lithium hydride additive is excessive, the composite density and cycle characteristics may be degraded. After the initial charge and discharge, a large amount of inactive additive remains in the cathode, which lowers the composite density of the cathode and acts as a kind of resistance layer, thereby degrading performance. Conversely, if the capacity ratio is 9 / 1 or more, that is, if the charge capacity of the lithium hydride additive is low, there is a problem in that the lifespan characteristics and initial efficiency are significantly degraded.

[0078] In particular, secondary batteries containing anode-less structures exhibit significant irreversible capacity loss and very low initial efficiency, requiring a lithium source to compensate for this. While methods exist to control the degree of capacity depletion by adjusting charge and discharge voltages, such approaches are limited because the voltage range at which capacity is depleted is very narrow for some cathode active materials.

[0079] The required capacity to be used at the negative electrode of a negative electrode secondary battery can be easily controlled through the capacity ratio defined by Equation 1 above. It is easy to optimize the lithium additive content in the positive electrode, and as a result, a negative electrode secondary battery with improved performance can be provided.

[0080] Referring to FIG. 6, the positive electrode after the formation step of the lithium secondary battery may contain a lithium-ion additive (LIA) in a delithiated state. That is, the lithium-ion additive (LRA) may exist in a delithiated state after the formation step. In one embodiment, the lithium-ion additive (LIA) in a delithiated state may include a compound of Chemical Formula 2 below.

[0081] [Chemical Formula 2]

[0082] Li a2 MO b2

[0083] In the above chemical formula 2, M is an element selected from the group consisting of Ni, Co, Al, Fe, and Mo, and 1≤a2≤4, 2≤b2<4. For example, a lithium additive in a delithiated state may include LiFeO2.

[0084] As described above, the lithium-ion additive (LIA) in a delithiated state may contain lithium released from the existing lithium-ion additive (LRA). That is, during the initial charging process, lithium within the lithium-ion additive (LRA) may be released to form the lithium-ion additive (LIA) in a delithiated state.

[0085] Lithium released from the positive electrode after the initial charge / discharge can be deposited as a lithium metal layer on the negative electrode current collector. This lithium metal layer can be used as a negative electrode active material. Furthermore, a lithium metal layer of a uniform thickness can provide sites for lithium electrodeposition during the subsequent operation of the battery. By providing sites for lithium electrodeposition, a uniform negative electrode active material layer can be maintained even with repeated continuous charge / discharge cycles. In addition, the lithium additive can replenish lithium that is depleted due to reactions with the electrolyte, the formation of the SEI layer, etc.

[0086] Subsequently, the lithium-ion additive (LIA) in the delithiated state may exist in an electrochemically inactive state lacking ion conductivity. In other words, the lithium-ion additive (LRA) may not be used as a cathode active material that reversibly absorbs and releases lithium ions. The lithium-ion additive (LRA) may transition to a delithiated state after the initial charge-discharge process and exist as an inert resistive material within the cathode. The average particle size of the lithium-ion additive (LIA) in the delithiated state may be smaller than or substantially the same as that of the conventional lithium-ion additive (LRA). The lithium-ion additive (LIA) in the delithiated state does not substantially participate in the battery's operation process and may degrade the performance of the cathode. Furthermore, the lithium-ion additive may reduce the composite density of the cathode active material layer.

[0087] In an embodiment of the present invention, the composite density of the cathode active material layer can be improved by controlling the daridium additive (LRA) to have an average particle size within a certain range. Additionally, the composite density of the cathode active material layer containing the daridium additive (LRA) can be improved by controlling both the average particle size of the cathode active material and the average particle size of the daridium additive (LRA).

[0088] Referring again to FIGS. 5 and 6, the positive active material layer of one embodiment may include a positive active material (CAC) and a lithium additive (LRA) of different average particle sizes. The average particle size may refer to the diameter (D50) of a particle in which the cumulative volume in the particle size distribution is 50 volume%. The average particle size may be a value measured by a particle size analyzer.

[0089] According to an embodiment of the present invention, to optimize the performance of a negative electrode secondary battery, a positive electrode active material layer having an optimal composition can be provided by controlling the particle size and content ratio. As a result, the stability and lifespan characteristics of the electrode plate can be simultaneously improved in a high-density, high-capacity negative electrode secondary battery.

[0090] The positive active material (CAC) may include a first particle (PTC1) of large diameter and a second particle (PTC2) of small diameter. The average particle size of the first particle (PTC1) may be larger than the average particle size of the second particle (PTC2). In one embodiment, the ratio of the average particle size of the first particle (PTC1) to the average particle size of the second particle (PTC2) may be 3 to 8. In one embodiment, the weight ratio of the first particle to the second particle may be 6:4 to 9:1. By satisfying the above ranges for the average particle sizes of the first and second particles (PTC1, PTC2), the composite density of the positive active material layer (120) can be improved. Additionally, the composite density of the positive active material layer can be improved through a structure in which the positive active material layer contains more of the first particle of large diameter, occupying most of the volume of the positive active material layer, while the second particle of small diameter fills the voids between the particles. The first and second particles (PTC1, PTC2) of the above range are mixed to improve the electrode plate bonding strength of the positive active material layer (120) and to provide a uniform positive. In one embodiment, the average particle size of the first particle (PTC1) may be 15 μm to 24 μm. In one embodiment, the average particle size of the second particle (PTC2) may be 4 μm to 8 μm.

[0091] The average particle size of the daridium additive (LRA) may be smaller than the average particle size of the cathode active material (CAC). That is, the average particle size of the daridium additive (LRA) may be smaller than the average particle size of the second particle (PTC2). In one embodiment, the average particle size of the second particle (PTC2) relative to the average particle size of the daridium additive (LRA) may be 1 to 3. In one embodiment, the average particle size of the daridium additive (LRA) may be 1 μm to 4 μm. By satisfying the above ranges for the average particle size of the daridium additive (LRA), the density of the composite can be improved without remaining as an excessive resistance layer within the cathode active material layer. In particular, a structure having an optimal density can be formed through the composition of a cathode active material layer in which the first and second particles and the daridium additive having different average particle sizes are mixed. Compared to a structure in which the three particles are simply mixed, the density of the composite increases and the lifespan characteristics of the electrode can be improved. In one embodiment, the composite density of the positive active material layer may be 3.5 g / cc to 4.0 g / cc. By including a positive electrode with improved composite density and electrode plate adhesion, the capacity and lifespan of a non-anode battery can be improved.

[0092] The positive electrode active material (CAC) is a material capable of reversibly absorbing and releasing lithium ions and may include lithium transition metal oxides or lithium transition metal phosphates. For example, the positive electrode active material (CAC) may include lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron phosphate oxide, as well as nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited to these. Additionally, the positive electrode active material may be a single material or a mixture of two or more materials. The shape of the positive electrode active material (CAC) may include particle shapes such as spheres or ellipsoids.

[0093] A positive electrode active material (CAC) according to one embodiment may include a layered lithium cobalt oxide (LCO) represented by the chemical formula 3 below.

[0094] [Chemical Formula 3]

[0095] Li a3 Co x3 A y3 O c3

[0096] In the above chemical formula 3, 1≤a3≤1.5, 0.9≤x3≤1.0, 0≤y3≤0.05, and 2≤c3≤2.3 may be present. A may be at least one element selected from the group consisting of Al, Ti, Ni, Mn, and Mg. A may be a dopant doped into the positive active material.

[0097] The aforementioned lithium cobalt oxide (LCO) has a layered structure, high electrical conductivity, and a rapid lithium ion diffusion rate. Furthermore, it contains relatively large single-crystal particles ranging from several to tens of micrometers, offering the advantage of high energy per unit volume. In particular, lithium cobalt oxide can provide the highest energy density among existing cathode materials, making it suitable for use primarily in small batteries. Additionally, lithium cobalt oxide exhibits a relatively stable charge-discharge voltage range, allowing for consistent battery performance. While cathode materials such as NCM, NCA, and NCMA exist that contain nickel, manganese, and aluminum in addition to cobalt, the lithium cobalt oxide (LCO) cathode may be advantageous in terms of efficiency for small batteries. Moreover, considering that the precipitated lithium metal is used as the anode active material, it may also be advantageous in terms of battery stability.

[0098] Lithium cobalt oxide (LCO) may be surface-treated to ensure stability under high voltage conditions. Lithium cobalt oxide (LCO) may be doped with a metal element to ensure surface and structural stability. In this case, the metal element may be one or more elements selected from Mg, K, Na, Ca, Si, Ti, Zr, Sn, Y, Sr, Mo, and Mn. Alternatively, the lithium cobalt oxide (LCO) may include a coating layer on its surface. The coating layer may cover the entire surface of the lithium cobalt oxide (LCO) or cover a portion of the surface. The coating layer may include at least one selected from the group consisting of a cobalt-containing compound, a titanium-containing compound, and an aluminum-containing compound.

[0099] FIGS. 7 and FIGS. 8 are SEM images showing the alleles and subparticles of lithium cobalt oxide, respectively. Referring to FIGS. 7 and FIGS. 8, lithium cobalt oxide may have a single particle form. In this specification, a single particle may mean a solitary particle that does not have internal particle boundaries. Morphologically, a single particle may mean a single particle, a monolithic structure, a monolithic structure, or a non-aggregated particle existing as an independent phase in which the particles are not mutually aggregated. As an example, the single particle may be a single crystal. As another example, the single particle may have a form in which a plurality of primary particles are attached to each other. Alternatively, the single particle may have a form in which 2 to 100 primary particles are attached to each other.

[0100] The positive active material layer (120) according to one embodiment may further include a binder and / or a conductive material in addition to the positive active material and the lithium additive described above.

[0101] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the positive current collector (110). As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0102] Examples of the above-mentioned non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or combinations thereof.

[0103] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0104] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0105] The above dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0106] The above conductive material is used to impart conductivity to the electrode, and any material that improves conductivity without causing chemical changes in the battery being constructed may be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0107] The positive current collector can provide a reference surface on which the positive active material layer is disposed. The positive current collector may include, for example, a plate or foil comprising indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof. To increase the bonding strength between the positive current collector and the positive active material layer, a carbon layer with a thickness of 0.1 μm to 4 μm may be further disposed between the positive current collector and the positive active material layer.

[0108]

[0109] An electrolyte layer (300) according to one embodiment may be provided between the anode (100) and the cathode (200). The electrolyte layer (300) may include a separator and an electrolyte. In one embodiment, the electrolyte may include at least one selected from a liquid electrolyte, a solid electrolyte, and a gel polymer electrolyte. In some cases, the separator may be omitted.

[0110] The separator may comprise a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate. The porous substrate may be a polymer membrane formed from any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these. The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer. The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include, but is not limited to, inorganic particles selected from SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The organic and inorganic materials may exist mixed in a single coating layer, or may exist in a stacked form in which a coating layer containing organic materials and a coating layer containing inorganic materials are stacked.

[0111] In one embodiment, the electrolyte layer (300) may include a liquid electrolyte. The liquid electrolyte may include a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent may serve as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0112] The above-mentioned non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0113] Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) may be used.

[0114] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0115] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, as ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0116] The above-mentioned non-aqueous organic solvent may be used alone or in a mixture of two or more types. In addition, when using a carbonate-based solvent, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0117] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0118] In one embodiment, the electrolyte layer (300) may include a gel polymer electrolyte. The gel polymer electrolyte may include a cross-linked polymer. The cross-linked polymer may be one in which cross-linkable monomers form a network and are cross-linked. The gel polymer electrolyte may further include a cross-linking agent, a photoinitiator, etc. to assist in the cross-linking of the cross-linkable monomers. The cross-linkable monomers, cross-linking agents, initiators, etc. are not particularly limited as long as they are commonly used in the art. Methods for forming the gel polymer electrolyte include curing using heat, UV, or high-energy radiation. The cross-linked polymer forms a cross-linked network, and a liquid electrolyte may be introduced into the formed cross-linked network. By introducing the liquid electrolyte into the cross-linked network, the exposure of the electrolyte to the electrode surface can be minimized, and a uniform flow of lithium ions can be created throughout the electrode. The composition of the liquid electrolyte within the gel polymer electrolyte may be substantially the same as the liquid electrolyte described above. Stability may be improved by incorporating the liquid electrolyte into the cross-linked network. Stability can be improved by suppressing electrochemical side reactions and electrolyte decomposition reactions occurring at the anode and cathode.

[0119] In one embodiment, the electrolyte layer (300) may include a solid electrolyte. The solid electrolyte may be, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may be, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li pMO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , 0≤x≤2, and one or more selected from. Sulfide-based solid electrolytes are produced by processing starting materials, such as Li2S or P2S5, by methods such as melt quenching or mechanical milling. Additionally, heat treatment may be performed after such processing. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. Furthermore, the solid electrolyte may include sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the sulfide-based solid electrolyte materials described above. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material comprising Li2S-P2S5 to form a solid electrolyte, the molar ratio of Li2S and P2S5 is, for example, in the range of Li2S : P2S5 = 20 : 80 to 90 : 10, 25 : 75 to 90 : 10, 30 : 70 to 70 : 30, and 40 : 60 to 60 : 40.

[0120] Sulfide-based solid electrolytes may include, for example, an argyrodite-type solid electrolyte represented by the following chemical formula A:

[0121] <Chemical Formula A>

[0122] Li + 12-n-x A n+ X 2- 6-x Y - x

[0123] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; X is S, Se, or Te; Y is Cl, Br, I, F, CN, OCN, SCN, or N3; and 1≤n≤5, 0≤x≤2. Sulfide-based solid electrolytes are, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x It may be an argyrodite-type compound containing one or more selected from 0≤x≤2. The sulfide-based solid electrolyte may be an argyrodite-type compound containing one or more selected from, for example, Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0124] Alternatively, sulfide-based solid electrolytes are Li 7-a M a PS 6-c X cIt may be an argyrodite-type compound containing (0≤a≤2, (0≤c≤2)). Here, X may be F, Br, Cl, or a combination thereof. M may be candium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof.

[0125] The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or higher, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the solid electrolyte layer by Li can be effectively suppressed. The elastic modulus of the solid electrolyte may be, for example, 15 GPa to 35 GPa.

[0126]

[0127] Method for manufacturing a lithium secondary battery

[0128] A method for manufacturing a lithium secondary battery according to an embodiment of the present invention may include manufacturing a positive electrode, manufacturing a negative electrode, assembling a lithium secondary battery by stacking the positive electrode and the negative electrode, and forming the lithium secondary battery.

[0129] Manufacturing a positive electrode may include preparing a positive electrode slurry and forming a layer of positive electrode active material on a positive electrode current collector. According to an embodiment of the present invention, the positive electrode slurry may include a positive electrode active material and a lithium anode additive. The positive electrode slurry may also be prepared by further mixing other additives, such as a conductive material and a binder. The positive electrode slurry may be prepared, for example, through a wet process using an organic solvent such as N-methyl-2-pyrrolidone (NMP), or through a dry process that does not require a solvent. The composition of the positive electrode slurry may be subject to the same description of the positive electrode of a lithium secondary battery as described above. For example, the positive electrode slurry may be a trimodal mixture in which a positive electrode active material of large particle size, a positive electrode active material of small particle size, and a lithium anode additive are mixed in a certain ratio.

[0130] A manufactured positive active material slurry can be applied to a positive current collector to a uniform thickness and dried to form a positive active material layer. At this time, equipment such as a doctor blade or a slot die coater may be used to form a uniform positive active material layer. After the positive active material slurry is applied, the solvent can be removed through a drying oven to form a solid positive active material layer. Conditions such as drying temperature and time can be adjusted according to the positive composition. In addition to the wet process described above, the manufacturing of the positive may also include a dry positive manufacturing process that does not contain organic solvents.

[0131] Subsequently, the dried positive electrode active material layer may be rolled to have a uniform thickness and density. By rolling the positive electrode active material layer, physical properties such as porosity and composite density of the positive electrode active material layer can be controlled. According to embodiments of the present invention, the composite density of the positive electrode active material layer can be improved by controlling the average particle size of the positive electrode active material and the lithium anode additive.

[0132] In addition, additional steps such as cutting the rolled positive active material layer to a desired size and connecting the uncoated portion of the positive current collector to the substrate tab may be included, but a detailed explanation is omitted as this is obvious to those skilled in the art.

[0133] The cathode according to an embodiment of the present invention has a cathode-free structure in which the cathode active material layer is omitted. That is, manufacturing the cathode may include preparing a cathode current collector.

[0134] Subsequently, the process may include assembling a lithium secondary battery by stacking each manufactured positive and negative electrode. In one embodiment, a lithium secondary battery may be assembled by stacking the positive and negative electrodes with a separator interposed between them, injecting a liquid electrolyte, and sealing. In another embodiment, a lithium secondary battery may be assembled by stacking the positive and negative electrodes with a solid electrolyte interposed between them.

[0135] A method for manufacturing a lithium secondary battery may further include forming the assembled lithium secondary battery. Forming the lithium secondary battery may include charging and discharging the lithium secondary battery to stabilize the battery.

[0136] A lithium metal layer can be formed on the negative electrode current collector by charging a lithium secondary battery. That is, a negative electrode active material layer can be formed by charging a negative electrode-free lithium secondary battery.

[0137] Discharging a lithium secondary battery may involve oxidizing a formed lithium metal layer. By oxidizing the lithium metal layer, lithium ions can move to the positive electrode to drive the battery. In other words, the lithium metal layer can be used as a negative electrode active material.

[0138] In addition, forming a lithium secondary battery may further include lithium moving within the positive electrode to form an SEI layer on the surface of the negative electrode. The formed SEI layer can act as a protective layer on the surface of the negative electrode to improve the stability of the battery.

[0139] A lithium secondary battery assembled according to the manufacturing method of the present invention may include a darium additive within the positive electrode. The darium additive is a lithium compound that additionally contains lithium in addition to the positive electrode active material and can replenish the irreversible capacity of the lithium secondary battery. Specifically, by including the darium additive in the positive electrode, the irreversible capacity generated during the manufacturing and use of the battery, including the formation of the lithium secondary battery, can be replenished. For example, irreversible capacity can be replenished by adjusting the charge / discharge voltage; however, in the case of a negative electrode-free lithium secondary battery such as the present invention, since an excess amount of lithium is consumed due to the formation of the negative electrode active material layer, using a darium additive may be more effective. Furthermore, depending on the type of positive electrode active material, the method of adjusting the charge / discharge voltage may be inappropriate.

[0140] The lithium additive within the anode can migrate to the cathode and be delithiated during the charging process of the lithium secondary battery. However, if lithium migrates to the cathode during the first charging process, the lithium additive can remain in a delithiated state. In other words, during the initial charging process, the lithium additive does not reversibly absorb the consumed lithium but can be electrochemically converted to an inactive state.

[0141] In one embodiment, the lithium additive prior to the formation step of a lithium secondary battery may include a compound of the following chemical formula 1.

[0142] [Chemical Formula 1]

[0143] Li a1 MO b1

[0144] In the above chemical formula 1,

[0145] M is an element selected from the group consisting of Ni, Co, Al, Fe, and Mo, and may be 2≤a1≤6, 2≤b1≤4. For example, the lithium additive may include Li5FeO4.

[0146] In one embodiment, the lithium additive after the formation step of a lithium secondary battery may include a compound of the following chemical formula 2.

[0147] [Chemical Formula 2]

[0148] Li a2 MO b2

[0149] In the above chemical formula 2,

[0150] M is an element selected from the group consisting of Ni, Co, Al, Fe, and Mo, and 1≤a2≤4, 2≤b2≤4.

[0151] In one embodiment, the lithium additive in a delithiated state may include a compound of the following chemical formula 4.

[0152] [Chemical Formula 4]

[0153] Li a4 FeO b4

[0154] In the above chemical formula 4, 1≤a4≤4 and 2≤b4<4 may be true.

[0155] For example, a lithium additive in a delithiated state may contain LiFeO2.

[0156] As described above, forming a lithium secondary battery may include charging the lithium secondary battery and discharging the lithium secondary battery. At this time, the operating voltage of the lithium secondary battery may be adjusted. For example, the operating voltage of the lithium secondary battery may be in the range of 2.8V to 4.6V or 3.0V to 4.5V. More specifically, the voltage at which the lithium secondary battery is charged and discharged may be adjusted. The voltage at which the charging of the lithium secondary battery is terminated may be 4V to 4.5V. Additionally, the voltage at which the discharging of the lithium secondary battery is terminated may be 2.5V to 3.2V.

[0157] By controlling the charge and discharge termination voltages, additional capacity can be expressed through the phase transition of the lithium additive. At the same time, excess lithium can be supplied to the negative electrode to form a negative electrode active material layer. The additionally supplied lithium can compensate for the irreversible capacity reduction of the negative electrode caused by lithium dendrite formation and dead lithium during the charge and discharge process, thereby improving the lifespan characteristics of the secondary battery.

[0158]

[0159] The creative idea described herein will be explained in more detail below through examples and comparative examples. However, the examples are merely illustrative and the scope of the creative idea described herein is not limited solely to these examples.

[0160] Examples and Comparative Examples: Manufacturing of Lithium Secondary Batteries

[0161] In a lithium secondary battery according to embodiments of the present invention, the positive electrode comprises a positive electrode active material layer comprising a first particle which is a large positive electrode active material, a second particle which is a small positive electrode active material, and a lithium additive. The particle size and content of each of the first and second particles and the lithium additive were varied for each embodiment to manufacture the positive electrode, and the results are summarized in Table 1 below.

[0162] LiCoO2 was used as the positive active material. The positive active material includes large and small particles. Li5FeO4 was used as the lithium additive. Except for the composition of the positive, PVdF was used as the binder and Super-P (Timcal Ltd.) was used as the conductive material to manufacture the positive. Specifically, the prepared positive slurry composition was coated onto an aluminum foil and dried at approximately 50°C, and then the dried product was dried under vacuum at approximately 120°C to manufacture the positive.

[0163] A lithium secondary battery (pouch cell) was manufactured by using only a copper current collector as the cathode, placing a PE separator with a thickness of about 18 μm between the anode and the cathode, and injecting and sealing a liquid electrolyte in which 0.6 M LiBF4 and 0.6 M LiDFOB were dissolved in a solvent in which FEC and DEC were mixed in a volume ratio of 1:2 into the battery.

[0164] Lithium secondary batteries according to various examples and comparative examples are shown together in Table 1 below.

[0165] Cathode Active Material Lithium Additive Capacity Ratio Type Large Particle Size Small Particle Size Range, Small Particle Ratio (Parts by Weight) Type Particle Size Example 1 LCO20 μm 5 μm 8:2 LFO3 μm 7 / 3 Example 2 LCO20 μm 5 μm 8:2 LFO3 μm 5 / 5 Example 3 LCO20 μm 5 μm 8:2 LFO3 μm 9 / 1 Comparative Example 1 LCO20 μm 5 μm 8:2 --- Comparative Example 2 ---- LFO10 μm Example 4 LCO20 μm 5 μm 8:2 LFO10 μm 7 / 3 Example 5 LCO20 μm 5 μm 8:2 LFO10 μm 5 / 5 Comparative Example 3 LCO20 μm 5 μm 8:2 LFO10 μm 3 / 7 Example 6 LCO20 μm 5 μm 6:4 LFO3 μm 7 / 3 Example 7LCO20 μm5 μm6:4LFO3 μm5 / 5 Comparative Example 4LCO20 μm5 μm6:4LFO3 μm3 / 7

[0166]

[0167] Evaluation Example 1: Anode particle analysis

[0168] Lithium cobalt oxide (LCO) was used as the positive electrode active material. Based on particle size, the particles were classified into first particles of large diameter and second particles of small diameter. An SEM image of the first particles is shown in Fig. 7a, and an SEM image of the second particles is shown in Fig. 7b. Although the first and second particles differ in average particle size, it can be confirmed that they are in the form of single particles with a size of several micrometers. It can be seen that both the first and second particles are either single crystals or in the form of multiple primary particles attached.

[0169] Lithium iron oxide (Li5FeO4, LFO) was used as a lithium-ion additive. SEM images of the lithium-ion additive are shown in Figures 8a and 8b. It can be confirmed that the lithium-ion additive is in the form of single particles with a smaller average particle size compared to the cathode active material.

[0170] Evaluation Example 2: Plate Analysis

[0171] FIGS. 9a to 10b show cross-sectional SEM images of anodes according to embodiments of the present invention. Specifically, FIGS. 9a and 9b show the anode of Example 1, and FIGS. 10a and 10b show the anode of Example 5.

[0172] In the case of the anode according to the examples, it can be seen that the particles within the anode have a structure in which they are densely packed. That is, it can be confirmed that the composite density of the anode according to the examples is higher. Furthermore, it can be seen that the composite density can be further improved by controlling the particle size range of the lithium hydride additive.

[0173] The pellet density of the anode mixtures of the examples and comparative examples was measured, and the results are shown in Table 2.

[0174] Pellet Density (g / cc) Example 13.81 Example 23.72 Example 33.89 Comparative Example 14.16 Comparative Example 21.85 Example 43.62 Example 53.41 Comparative Example 33.1 Example 63.77 Example 73.68 Comparative Example 43.43

[0175] In the case of Comparative Example 1, the composite density of the anode not containing a lithium additive shows the highest value. In the case of Comparative Example 2, the composite density of the lithium additive shows a very low value. That is, it can be confirmed that it is generally the case that the composite density decreases when a lithium additive is included in the anode.

[0176] Referring to the results of comparing Examples 4 and 5 with Comparative Example 3 and the results of comparing Examples 6 and 7 with Comparative Example 4, respectively, it indicates that the particle size of the cathode active material and the particle size of the lithium additive were adjusted to be the same, and only the capacity ratio was adjusted. It can be seen that the density of the composite material in Examples 4 and 5 is higher than that in Comparative Example 3, and the density of the composite material in Examples 6 and 7 is higher than that in Comparative Example 4.

[0177] In addition, according to the embodiments, it can be seen that the density of the composite is improved by controlling the average particle size of the particles within the anode. An optimal anode can be provided by controlling the particle size ratio of each average particle size. As a result, a battery with improved energy density can be provided by increasing the density of the composite.

[0178] Evaluation Example 3: Battery Characteristics Evaluation

[0179] The characteristics of the lithium secondary battery according to the preceding examples and comparative examples were evaluated.

[0180] The manufactured lithium secondary battery was charged with a constant current at a rate of 0.1C at 45℃ until the voltage reached 4.50V (vs. Li), and then cut off at a rate of 0.05C while maintaining 4.50V in constant voltage mode. Subsequently, it was discharged with a constant current of 0.1C until the voltage reached 2.8V (vs. Li) during discharge.

[0181] The formation process was completed by performing this charge-discharge process once.

[0182] A lithium secondary battery that has undergone the formation stage was charged at 45°C at a constant current of 0.33C within a voltage range of 3.0 to 4.5V relative to lithium metal, and then cut off at a current rate of 0.05C while maintaining 4.50V in constant voltage mode. Subsequently, constant current discharge was performed at 1.0C until a cut-off voltage of 3.0 was reached. The aforementioned charge-discharge process was repeated a total of 100 times. In each charge-discharge cycle, a 5-minute pause was observed after each charge / discharge cycle. Here, the capacity retention rate in the Nth cycle is defined by the following mathematical formula.

[0183] [Mathematical Formula 1]

[0184] Capacity Retention Rate (%) = (Capacity of Nth Cycle) / (Capacity of 1st Cycle) × 100

[0185] Based on the initial charge / discharge capacity, the capacity after 100 cycles was evaluated.

[0186] Volume Retention Rate (%, @100cyc) Example 193.5 Example 290.7 Example 391.0 Comparative Example 139.9 Comparative Example 20 Example 471.0 Example 564.9 Comparative Example 358.2 Example 676.8 Example 770.6 Comparative Example 465.4

[0187] Referring to Table 3, it can be seen that the capacity retention rates of the embodiments are higher than those of the comparative examples. In particular, it can be seen that the capacity retention rate is significantly lower in the case of a cathode that does not contain a lithium anode additive, such as in Comparative Example 1. This implies that the loss due to the irreversible capacity of the anode-free battery is very large. Furthermore, it can be seen that lifespan characteristics deteriorate when the capacity of the lithium anode additive increases beyond a certain level relative to the cathode active material, as in Comparative Examples 3 and 4. This means that if an excess amount of the lithium anode additive remains in the cathode after the lithium has been consumed, it acts as an inactive material that actually degrades performance. It can be seen that the cathode according to the embodiments of the present invention provides an optimal composition for providing a long-life anode-free secondary battery by controlling the capacity ratio of the cathode active material and the lithium anode additive.

Claims

1. A positive current collector, and a positive active material layer on the positive current collector; A cathode comprising a cathode current collector; and The electrolyte layer between the anode and the cathode, wherein The above positive active material layer is: A positive active material comprising a first particle of large particle size and a second particle of small particle size; and It contains a lithium additive, A lithium secondary battery having a capacity ratio of the positive electrode active material and the lithium additive evaluated by Formula 1 below of 5 / 5 to 9 / 1: [Equation 1] Capacity ratio = {(Discharge capacity per unit mass of positive active material (mAh / g)) / (Charge capacity per unit mass of lithium additive (mAh / g))} In the above Equation 1, the charging capacity of the lithium additive is defined by the following Equation 2, [Equation 2] Charging capacity per unit mass of lithium additive (mAh / g) = [{Total charging capacity of the anode (mAh) - Charging capacity of the anode active material (mAh)} / Loading amount of lithium additive (g)].

2. In Paragraph 1, The weight ratio of the first particle to the second particle is 6:4 to 9:1, Lithium secondary battery.

3. In Paragraph 1, The ratio of the average particle size of the first particle to the average particle size of the second particle is 3 to 8, Lithium secondary battery.

4. In Paragraph 1, The average particle size of the above lithium additive is smaller than the average particle size of the above second particle, and The ratio of the average particle size of the second particle to the average particle size of the lithium additive is 1 to 3, Lithium secondary battery.

5. In Paragraph 1, The above positive active material comprises a compound of the following chemical formula 3, Lithium secondary battery: [Chemical Formula 3] Li a3 Co x3 A y3 O c3 In the above chemical formula 3, 1≤a3≤1.5, 0.9≤x3≤1.0, 0≤y3≤0.05, 2≤c3≤2.3, and A is at least one element selected from the group consisting of Al, Ti, Ni, Mn and Mg.

6. In Paragraph 1, The above-mentioned lithium additive comprises a compound of the following chemical formula 1, Lithium secondary battery: [Chemical Formula 1] Li a1 MO b1 In the above chemical formula 1, M is an element selected from the group consisting of Ni, Co, Al, Fe, and Mo, and 2≤a1≤6, 2≤b1≤4.

7. In Paragraph 6, The above lithium additive comprises Li5FeO4, Lithium secondary battery.

8. In Paragraph 1, It further includes a lithium metal layer on the above-mentioned negative current collector, and The above lithium metal layer comprises lithium or a lithium alloy, Lithium secondary battery.

9. A positive current collector, and a positive active material layer on the positive current collector; A cathode comprising a cathode current collector and a lithium metal layer on the cathode current collector; and It includes an electrolyte layer disposed between the anode and the cathode, The above positive active material layer comprises a positive active material and a lithium additive in a delithiated state, and The average particle size of the above lithium additive is smaller than the average particle size of the above positive active material, and The above-mentioned lithium additive is represented by the following chemical formula 2, Lithium secondary battery: [Chemical Formula 2] Li a2 MO b2 In the above chemical formula 2, M is an element selected from the group consisting of Ni, Co, Al, Fe, and Mo, and 1≤a2≤4, 2≤b2<4.

10. In Paragraph 9, The above positive active material comprises a compound of the following chemical formula 3, Lithium secondary battery: [Chemical Formula 3] Li a3 Co x3 A y3 O c3 In the above chemical formula 3, 1≤a3≤1.5, 0.9≤x3≤1.0, 0≤y3≤0.05, 2≤c3≤2.3, and A is at least one element selected from the group consisting of Al, Ti, Ni, Mn and Mg.

11. In Paragraph 9, The average particle size of the above lithium additive is 1 μm to 4 μm, Lithium secondary battery.

12. In Paragraph 9, The above positive active material comprises a first particle of large diameter and a second particle of small diameter, and The ratio of the average particle size of the first particle to the average particle size of the second particle is 3 to 8, Lithium secondary battery.

13. In Paragraph 12, The weight ratio of the first particle and the second particle is 6:4 to 9:1, Lithium secondary battery.

14. In Paragraph 9, The above lithium secondary battery is characterized by having completed the initial charge / discharge process, Through the above initial charge / discharge process, the lithium metal layer and the lithium additive in the delithiated state are formed, Lithium secondary battery.

15. Manufacturing the anode; Manufacturing a cathode; Assembling a lithium secondary battery by stacking the anode and the cathode; and Including the formation of a lithium secondary battery, The above-mentioned anode comprises an anode active material and a lithium additive, and The above cathode includes a cathode current collector, and Forming the above lithium secondary battery is: Charging the above lithium secondary battery to form a lithium metal layer on the above negative electrode current collector; and It includes discharging the lithium secondary battery to oxidize the lithium metal layer, and After the above discharge is terminated, the above lithium additive has a delithiated state, Method for manufacturing a lithium secondary battery.

16. In Paragraph 15, The above lithium additive includes Li5FeO4, and The above-mentioned lithium additive in a delithiated state comprises a compound of the following chemical formula 4, Method for manufacturing lithium secondary batteries: [Chemical Formula 4] Li a4 FeO b4 In the above chemical formula 4, 1≤a4≤4 and 2≤b4<4.

17. In Paragraph 15, The capacity ratio of the positive electrode active material and the lithium additive calculated by the following Formula 1 is 5 / 5 to 9 / 1, Method for manufacturing lithium secondary batteries: [Equation 1] Capacity ratio = {(Discharge capacity per unit mass of positive active material (mAh / g)) / (Charge capacity per unit mass of lithium additive (mAh / g))} In the above Equation 1, the charging capacity of the lithium additive is defined by the following Equation 2. [Equation 2] Charging capacity per unit mass of lithium additive (mAh / g) = [{Total charging capacity of the cathode (mAh) - Charging capacity of the cathode active material (mAh)} / Loading amount of lithium additive (g)] 18. In Paragraph 15, The voltage at which charging of the above lithium secondary battery ends is 4V to 4.5V, and The voltage at which the discharge of the above lithium secondary battery ends is 2.5V to 3.2V, Method for manufacturing a lithium secondary battery.

19. In Paragraph 15, The above positive active material comprises a compound of the following chemical formula 3, Method for manufacturing lithium secondary batteries: [Chemical Formula 3] Li a3 Co x3 A y3 O c3 In the above chemical formula 3, 1≤a3≤1.5, 0.9≤x3≤1.0, 0≤y3≤0.05, 2≤c3≤2.3, and A is at least one element selected from the group consisting of Al, Ti, Ni, Mn and Mg.

20. In Paragraph 15, The average particle size of the above lithium additive is smaller than the average particle size of the above positive active material, Method for manufacturing a lithium secondary battery.

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