Secondary Battery Manufacturing Method with Divided Injection of Electrolyte and Secondary Battery with Improved Cycle Characteristics

Abstract

The present invention provides a secondary battery with improved cycle characteristics through split injection of the electrolyte and a method for manufacturing the same.

Description

Technology Field

[0001] The present invention relates to a secondary battery and a method for manufacturing the same, and more specifically, to a secondary battery with improved cycle characteristics through split injection of an electrolyte and a method for manufacturing the same. Background Technology

[0003] With the increasing technological development and demand for mobile devices, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Recently, as lithium-ion batteries are being used as power sources for medium and large-sized devices such as electric vehicles, high capacity and high energy density are required, and furthermore, excellent cycle characteristics are also required.

[0005] Looking at the manufacturing process of secondary batteries, the electrode assembly is loaded into a battery case, and then the electrolyte is filled. The electrolyte contains various additives, and during the initial charging and discharging process, these additives decompose to form a film on the surface of the electrode active material. This film formed on the surface of the electrode active material plays a role in increasing electrode durability and improving the battery's cycle characteristics. Furthermore, the decomposition of electrolyte additives generates a large amount of gas. The generated gas inside the battery causes a decrease in battery efficiency and durability.

[0006] As the specifications required for secondary batteries increase, there is a growing need for technology that forms a more stable and robust film on the surface of the electrode active material while suppressing the amount of gas trapped inside the battery. Prior art literature

[0008] U.S. Patent Publication No. 2018-0316040 The problem to be solved

[0009] Accordingly, the objective of the present invention is to provide a secondary battery with improved cycle characteristics through split injection of the electrolyte and a method for manufacturing the same. means of solving the problem

[0011] In order to solve the aforementioned problem,

[0012] In one embodiment, the present invention comprises: a first electrolyte injection step of injecting a first electrolyte containing a first additive into a battery case housing an electrode assembly and charging the battery to SOC S1%; and an Nth electrolyte containing an Nth additive into a battery case housing an electrode assembly and charging the battery to SOC S N It includes a step of injecting an Nth electrolyte to charge up to %. Here, N is an integer between 2 and 10. In addition, the method for manufacturing a secondary battery according to the present invention satisfies the following condition 1.

[0013] [Condition 1]

[0014] SOC S K+1 % > SOC S K %

[0015] In condition 1, K is an integer between 1 and N-1.

[0017] In another embodiment, the method for manufacturing a secondary battery according to the present invention comprises, in the K-th electrolyte injection step performed between the first electrolyte injection step and the N-th electrolyte injection step, injecting a K-th electrolyte containing a K-th additive into a battery case housing an electrode assembly and the battery SOC S K Charge up to %. Here, SOC S K % The battery voltage during charging is V K It is. In addition, the above-mentioned additive K has a voltage range V in which it reacts with the electrode within the electrolyte. K It includes one or more additives as follows.

[0018] In one specific embodiment, in the first electrolyte injection step, the electrolyte injection rate is in the range of 40 to 95% (V / V).

[0019] In one embodiment, N is 2, and the first additive comprises one or more additives having a voltage range of 1.5 to 2.5 V that reacts with the electrode in the electrolyte, and the second additive comprises one or more additives having a voltage range of greater than 2.5 and less than or equal to 4.2 V that reacts with the electrode in the electrolyte.

[0020] In a specific embodiment, the first additive comprises one or more of VEC (Vinyl ethylene carbonate) and PRS (1,3-proene soltone). Additionally, the second additive comprises one or more of PS (1,3-propane soltone) and VC (Vinylene carbonate).

[0021] In one embodiment, the present invention includes an activation step for the battery after the Nth electrolyte injection step.

[0022] In a specific embodiment, the present invention sequentially performs a first electrolyte injection step; a degas step for removing gas generated inside the battery; a second or subsequent electrolyte injection step; and an activation step.

[0023] In one embodiment, any one or more of the first to Nth electrolytes in the present invention comprises a non-aqueous organic solvent. Specifically, the non-aqueous organic solvent is a carbonate-based organic solvent comprising any one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0024] For example, the secondary battery according to the present invention is a pouch-type lithium secondary battery.

[0026] In addition, the present invention provides a secondary battery manufactured by the manufacturing method described above. In one embodiment, the secondary battery according to the present invention comprises an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a battery case housing the electrode assembly; and an electrolyte injected into the battery case. Furthermore, the electrode active material included in the negative electrode has a structure in which a Solid Electrolyte Interphase (SEI) film is formed. Effects of the invention

[0028] The lithium secondary battery according to the present invention includes a specific over-lithium oxide as a positive additive in the positive composite layer and includes a specific additive compound in the electrolyte, so as to improve the degradation of battery capacity due to irreversible reactions of the battery, as well as achieve low electrical resistance of the electrode and high charge / discharge capacity, it can be usefully used in fields requiring high-speed charging and / or high capacity. Brief explanation of the drawing

[0030] FIG. 1 is a flowchart illustrating a secondary battery manufacturing process according to one embodiment of the present invention. Specific details for implementing the invention

[0031] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are to be described in detail in the detailed description.

[0032] However, this is not intended to limit the invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0033] In the present invention, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0034] Furthermore, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "immediately above" the other part, but also cases where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only cases where it is "immediately below" the other part, but also cases where there is another part in between. Additionally, in the present application, being "placed on" may include cases where it is placed on the lower part as well as on the upper part.

[0036] The present invention will be described in more detail below.

[0038] In one embodiment, the present invention comprises: a first electrolyte injection step of injecting a first electrolyte containing a first additive into a battery case housing an electrode assembly and charging the battery to an SOC of 1%; and an Nth electrolyte containing an Nth additive into a battery case housing an electrode assembly and charging the battery to an SOC of 1%. N It includes an Nth electrolyte injection step that charges up to %. The present invention is characterized by performing the electrolyte injection in two or more divided steps. Specifically, N is an integer between 2 and 10, and satisfies the following condition 1.

[0039] [Condition 1]

[0040] SOC S K+1 % > SOC S K %

[0041] In condition 1, K is an integer between 1 and N-1.

[0042] According to Condition 1 above, the secondary battery manufacturing method according to the present invention increases the SOC of the battery sequentially or continuously, and accordingly, the voltage of the battery also increases. Depending on the type of additive contained in the electrolyte, the voltage range in which it reacts with the electrode in the electrolyte varies.

[0043] In the present invention, the term 'voltage at which the additive reacts with the electrode in the electrolyte' refers to a voltage at which the decomposition reaction of the additive is initiated when a specific voltage is applied under electrolyte conditions. Specifically, the additive described above decomposes under specific voltage conditions in the electrolyte to form a film of the electrode active material.

[0044] In one embodiment, the present invention comprises, in a K-th electrolyte injection step performed between a first electrolyte injection step and an N-th electrolyte injection step, injecting a K-th electrolyte containing a K-th additive into a battery case housing an electrode assembly and scaling the battery to SOC S K Charge up to %. In this case, SOC S K % The battery voltage during charging is V K And, the above-mentioned additive K has a voltage range V that reacts with the electrode in the electrolyte. K It includes one or more additives as follows. In the present invention, the voltage range in which the additive K reacts with the electrode in the electrolyte is V K It includes one or more additives as shown below, wherein the voltage range reacting with the electrode in the electrolyte is V K It does not exclude the inclusion of additional additives in excess.

[0045] As the SOC of the battery increases, the voltage of the battery increases. In the present invention, by sequentially introducing additives that decompose under conditions below the battery voltage, the film of the electrode active material is induced to be formed more stably.

[0046] In addition, the present invention has confirmed that it is more efficient to perform most of the electrolyte injection in the first electrolyte injection step and fill the remaining electrolyte in subsequent electrolyte injection steps. In the present invention, an excess amount of electrolyte is injected in the first electrolyte injection step, and a degas step can be performed thereafter. Through this, the gas generated from the electrolyte injected in the first step is effectively removed.

[0047] In a specific embodiment, in the first electrolyte injection step, the electrolyte injection rate is in the range of 40 to 95% (V / V). Specifically, in the first electrolyte injection step, the electrolyte injection rate is in the range of 45 to 90% (V / V), 50 to 90% (V / V), 45 to 70% (V / V), 70 to 90% (V / V), or 75 to 85% (V / V). For example, the present invention can complete the electrolyte injection by injecting 70 to 80% (V / V) of the electrolyte in the first electrolyte injection step and injecting 20 to 30% (V / V) of the electrolyte in the second electrolyte injection step.

[0048] In one embodiment, N is 2, and the first additive comprises one or more additives having a voltage range of 1.5 to 2.5 V that reacts with the electrode in the electrolyte. Additionally, the second additive comprises one or more additives having a voltage range of greater than 2.5 and less than or equal to 4.2 V that reacts with the electrode in the electrolyte.

[0049] In a specific example, the first additive comprises one or more of VEC (Vinyl ethylene carbonate) and PRS (1,3-propane soltone). Additionally, the second additive comprises one or more of PS (1,3-propane soltone) and VC (Vinylene carbonate). In this case, additives such as VEC and PRS undergo a decomposition reaction under relatively low voltage conditions, while additives such as PS and VC undergo a decomposition reaction under relatively high voltage conditions. In the present invention, the additive that undergoes a decomposition reaction under low voltage conditions is introduced first to induce stable film formation. Then, the additive that undergoes a decomposition reaction under high voltage conditions is introduced. In the present invention, through the split injection of the electrolyte, it is possible to achieve the formation of a film on the surface of the electrode active material that is more stable and highly durable, which leads to an improvement in the cycle characteristics of the battery.

[0050] In the present invention, it is possible to perform an activation step after the split injection of the electrolyte described above. In one embodiment, the present invention includes an activation step for the battery after the Nth electrolyte injection step.

[0051] In a specific embodiment, the method for manufacturing a secondary battery according to the present invention sequentially performs a first electrolyte injection step; a degas step for removing gas generated inside the battery; a second or subsequent electrolyte injection step; and an activation step. In the present invention, a large amount of gas is generated as additives contained in the electrolyte introduced through the first electrolyte injection step decompose. The generated gas is removed through the degas step. A second or subsequent electrolyte injection step is performed to replenish a small amount of electrolyte inside the battery from which the gas has been removed. Through this, the generation of gas inside the battery can be effectively suppressed.

[0052] In one embodiment, any one or more of the first to Nth electrolytes comprises a non-aqueous organic solvent. Specifically, the non-aqueous organic solvent is a carbonate-based organic solvent comprising any one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). For example, each of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) may be used in a range of about 20 to 40% (V / V). As a more specific example, ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) may be applied in a volume ratio of 1:1:1.

[0053] Furthermore, the secondary battery manufacturing method of the present invention is applicable to various rechargeable batteries. For example, the secondary battery is a pouch-type lithium secondary battery. The secondary battery manufacturing method according to the present invention enables effective removal or suppression of gas generation inside the battery while simultaneously forming a stable film on the surface of the electrode active material.

[0055] FIG. 1 is a flowchart illustrating a secondary battery manufacturing process according to one embodiment of the present invention. Referring to FIG. 1, the secondary battery manufacturing method according to the present invention comprises: a first electrolyte injection step (S10) of injecting a first electrolyte containing a first additive into a battery case housing an electrode assembly; a first charging step (S20) of charging the battery to SOC S1%; a gas removal step (S30) of removing gas generated inside the battery; an Nth electrolyte injection step (S40) of injecting an Nth electrolyte containing an Nth additive into a battery case housing an electrode assembly; and charging the battery to SOC S N It includes a step of charging up to % (S50) and a battery activation step (S60).

[0056] In one example, in the first electrolyte injection step (S10), 80% (V / V) of the electrolyte is injected and the SOC 10% charging step (S20) is performed. Then, after removing the gas generated inside the battery (S30), the second electrolyte injection step (S40) is performed and the step of charging to SOC 30% (S50) is performed. Then, the activation step (S60) for the battery is performed.

[0057] For example, if the electrolyte injection is performed in three stages, S40 and S50 are repeated twice. In this case, in the second electrolyte injection stage (S40-1), 10% (V / V) of the electrolyte is injected and the SOC is charged to 20% (S50-1). Then, in the third electrolyte injection stage (S40-2), 10% (V / V) of the electrolyte is injected and the SOC is charged to 30% (S50-2).

[0059] In addition, the present invention provides a secondary battery manufactured by the method described above. In one embodiment, the secondary battery according to the present invention comprises: an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a battery case housing the electrode assembly; and an electrolyte injected into the battery case. Furthermore, the electrode active material included in the negative electrode has a structure in which an SEI film is formed.

[0063] Specifically, the secondary battery according to the present invention includes a positive electrode and a negative electrode, and a separator may be placed between the positive electrode and the negative electrode, or the separator may be excluded. In addition, the positive electrode and the negative electrode contain lithium ions (Li) that are carried out between them. + It has a structure impregnated with an electrolyte for the movement of ).

[0064] At this time, the anode comprises an anode composite layer prepared by applying, drying, and pressing an anode slurry containing an anode active material and an anode additive onto an anode current collector, and the anode composite layer may optionally further include a conductive material, an organic binder polymer, an additive, etc. as needed.

[0065] At this time, the positive electrode active material may comprise a lithium metal composite oxide comprising three or more elements selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al), and the lithium metal composite oxide may, in some cases, include another transition metal (M 1 It may have a doped form. For example, the positive electrode active material may be a lithium metal composite oxide represented by the following chemical formula 1 capable of reversible intercalation and deintercalation:

[0066] [Chemical Formula 1]

[0067] Li x [Ni y Co z M 1 v ]O w

[0068] In the above chemical formula 1,

[0069] M 1 is one or more elements selected from the group consisting of Mn, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0070] x, y, z, w, v, and u are 1.0≤x≤1.30, 0.1≤y<0.95, and 0.01, respectively. <z≤0.5, 0≤v≤0.2, 1.5≤w≤4.5이다.

[0071] More specifically, the above positive active material is Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.7 Co 0.15 Mn 0.15 )O2, Li(Ni0.8 Co 0.1 Mn 0.1 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O2, Li(Ni 1 / 3 Co 1 / 3 Al 1 / 3 )O2, Li(Ni 0.6 Co 0.2 Al 0.2 )O2, Li(Ni 0.5 Co 0.2 Al 0.3 )O2, Li(Ni 0.7 Co 0.15 Al 0.15 )O2, Li(Ni 0.8 Co 0.1 Al 0.1 )O2 and Li(Ni 0.8 Co 0.1 Mn 0.05 Al 0.05 It may include one or more types selected from the group consisting of )O2.

[0072] As an example, the above-mentioned positive active material is a lithium metal composite oxide represented by Chemical Formula 4, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 or Li(Ni 0.8 Co 0.1 Al 0.1 )O2 can be used individually or in combination.

[0073] In addition, the content of the above-mentioned positive active material may be 85 to 95 parts by weight per 100 parts by weight of the composite layer, and specifically, may be 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight.

[0074] In addition, the anode composite layer comprises an anode active material exhibiting electrical activity and an anode additive that imparts irreversible capacity, and the anode additive may comprise a lithium metal oxide represented by the following chemical formula 2:

[0075] [Chemical Formula 2]

[0076] Li x Co 1-y Zn y O4

[0077] In the above chemical formula 2, x and y are 5≤x≤7 and 0≤y≤0.4, respectively.

[0078] The above-mentioned cathode additive may provide lithium ions to compensate for the lithium ion consumption caused by irreversible chemical and physical reactions at the anode during initial charging by containing an excess amount of lithium. Accordingly, the charging capacity of the battery may increase and the irreversible capacity may decrease, thereby improving lifespan characteristics. As such a cathode additive, the present invention may include one or more of the lithium metal oxides represented by Chemical Formula 2.

[0079] The lithium metal oxide represented by Chemical Formula 2 above has a higher lithium ion content compared to nickel-containing oxides commonly used in the industry. Since this allows for the replenishment of lithium ions lost due to irreversible reactions during the initial activation of the battery, the charge and discharge capacity of the battery can be significantly improved. Examples of such lithium metal oxides represented by Chemical Formula 2 include Li6CoO4 and Li6Co 0.5 Zn 0.5 O4, Li6Co 0.7 Zn 0.3 It may include O4, etc.

[0080] In addition, the content of the anode additive may be 1 weight% or less with respect to the total weight of the anode active material, and specifically, may be 0.01 to 1 weight%; 0.1 to 0.9 weight%; 0.3 to 0.9 weight%; 0.2 to 0.7 weight%; or 0.5 to 0.9 weight%.

[0081] Furthermore, the composite layer may further include a conductive material, a binder, an additive, etc., along with the positive electrode active material and the positive electrode additive. In this case, the conductive material may be used to improve performance such as the electrical conductivity of the positive electrode, and one or more carbon-based materials selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber may be used. For example, the conductive material may include acetylene black.

[0082] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the composite layer, and specifically, 0.5 to 5 parts by weight; 1 to 3 parts by weight; or 0.5 to 2 parts by weight of the conductive material.

[0083] In addition, the binder may include one or more resins selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As one example, the binder may include polyvinylidenefluoride.

[0084] In addition, the above binder may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the total anode composite layer, specifically 2 to 8 parts by weight; 1 to 5 parts by weight; or 1 to 3 parts by weight of a conductive material.

[0085] In addition, the average thickness of the anode composite layer is not particularly limited, but specifically may be 100㎛ to 200㎛, and more specifically may be 100㎛ to 200㎛; 100㎛ to 150㎛; 120㎛ to 170㎛; 150㎛ to 200㎛; or 150㎛ to 190㎛.

[0086] In addition, the anode may be used as an anode current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, surface-treated materials such as carbon, nickel, titanium, silver, etc. may be used. Furthermore, the anode current collector may have fine irregularities formed on its surface to increase the adhesion of the anode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible. Moreover, the average thickness of the current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured anode.

[0088] In addition, the above-mentioned cathode is manufactured by applying, drying, and pressing a cathode active material onto a cathode current collector, and may optionally further include a conductive material, a binder, etc., included in the anode composite layer as needed.

[0089] Here, the cathode active material may include a carbon material and a silicon material. The carbon material refers to a carbon material having carbon atoms as its main component. Such carbon materials may include graphite, which has a completely layered crystal structure like natural graphite; soft carbon, which has a low-crystallinity layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers); hard carbon, in which such structures are mixed with amorphous portions; artificial graphite; expanded graphite; carbon fiber; non-graphitized carbon; carbon black; acetylene black; ketjen black; carbon nanotubes; fullerene; activated carbon; graphene; carbon nanotubes; and, preferably, one or more selected from the group consisting of natural graphite, artificial graphite, graphene, and carbon nanotubes. More preferably, the carbon material may include natural graphite and / or artificial graphite, and together with the natural graphite and / or artificial graphite, may include one or more of graphene and carbon nanotubes. In this case, the carbon material may comprise 0.1 to 10 parts by weight of graphene and / or carbon nanotubes per 100 parts by weight of the total carbon material, and more specifically, may comprise 0.1 to 5 parts by weight or 0.1 to 2 parts by weight of graphene and / or carbon nanotubes per 100 parts by weight of the total carbon material.

[0090] In addition, the silicon material is a particle containing silicon (Si) as the main component as a metallic component, and may include silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or a mixture of these particles. Furthermore, the silicon material may have a form in which crystalline particles and amorphous particles are mixed, and the ratio of the amorphous particles may be 50 to 100 parts by weight, specifically 50 to 90 parts by weight; 60 to 80 parts by weight; or 85 to 100 parts by weight, based on 100 parts by weight of the total silicon material. By controlling the ratio of amorphous particles included in the silicon material to the above range, the present invention can improve thermal stability and flexibility without degrading the electrical properties of the electrode.

[0091] In addition, the above-mentioned negative electrode active material comprises a carbon material and a silicon material, and may include 80 to 99 parts by weight of the carbon material and 1 to 20 parts by weight of the silicon material per 100 parts by weight of the total.

[0092] More specifically, the negative electrode active material may contain, based on 100 parts by weight of the total, 80 to 95 parts by weight of a carbon material and 5 to 20 parts by weight of a silicon material; 90 to 97 parts by weight of a carbon material and 3 to 10 parts by weight of a silicon material; 85 to 92 parts by weight of a carbon material and 8 to 15 parts by weight of a silicon material; 82 to 87 parts by weight of a carbon material and 13 to 18 parts by weight of a silicon material; or 93 to 98 parts by weight of a carbon material and 2 to 7 parts by weight of a silicon material. By controlling the content of the carbon material and the silicon material included in the negative electrode active material to the above ranges, the present invention can improve the charge capacity per unit mass while reducing lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery.

[0093] In addition, the cathode composite layer may have an average thickness of 100㎛ to 300㎛, and specifically, may have an average thickness of 100㎛ to 250㎛, 100㎛ to 200㎛, 100㎛ to 180㎛, 100㎛ to 150㎛, 120㎛ to 200㎛, 140㎛ to 200㎛, or 140㎛ to 160㎛.

[0094] In addition, the above-mentioned negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. may be used, and in the case of copper or stainless steel, surface-treated carbon, nickel, titanium, silver, etc. may be used. Furthermore, similar to the positive electrode current collector, the above-mentioned negative electrode current collector may form fine irregularities on its surface to strengthen the bonding force with the negative electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible. In addition, the average thickness of the above-mentioned negative electrode current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured negative electrode.

[0096] In addition, the separator may be interposed between the anode and the cathode, in which case an insulating thin film having high ion permeability and mechanical strength may be used. The separator is not particularly limited as long as it is commonly used in the industry, but specifically, a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene; glass fiber; or polyethylene may be used, and in some cases, a composite separator in which inorganic particles / organic particles are coated by an organic binder polymer on a porous polymer substrate such as the sheet or nonwoven fabric may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator. Furthermore, the pore diameter of the separator may be an average of 0.01 to 10 μm, and the thickness may be an average of 5 to 300 μm.

[0097] Meanwhile, the above positive and negative electrodes may be wound into a jelly roll form and stored in a cylindrical battery, a prismatic battery, or a pouch-type battery, or stored in a pouch-type battery in a folding or stack-and-folding form, but are not limited thereto.

[0099] Furthermore, the above electrolyte may be in a state where a lithium salt and an additive are dissolved in the electrolyte solution. In addition, the above electrolyte solution may include a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0100] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. may be used.

[0101] The above organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociator, etc.

[0102] As the above-mentioned inorganic solid electrolyte, for example, nitrides, halides, sulfates of Li such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc., may be used.

[0103] The above lithium salt may be used without particular limitation as long as it is commonly used in the industry, and specifically, as a material that dissolves well in a non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylboronicate, imide, etc. may be used.

[0104] In addition, for the purpose of improving charge / discharge characteristics and flame retardancy, the electrolyte may be further enriched with, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, to impart non-flammability, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further enriched, carbon dioxide gas may be further enriched to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene Sultone), etc.

[0106] The present invention will be explained in more detail below through examples and experimental examples.

[0107] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0109] Examples 1–2 and Comparative Examples 1–4. Preparation of lithium secondary batteries

[0110] N-methylpyrrolidone solvent is injected into a homo mixer, and LiNi, the cathode active material, is 0.6 Co 0.2 Mn 0.2 6 parts by weight of O296, 2 parts by weight of carbon black as a conductive material, and 2 parts by weight of PVdF as a binder were each weighed and added, and mixed at 3,000 rpm for 60 minutes to prepare an anode forming slurry. The prepared anode forming slurry was applied to one side of an aluminum current collector, then dried at 100°C and rolled to manufacture an anode. At this time, the total thickness of the anode composite layer was 130 μm, and the total thickness of the manufactured anode was approximately 200 μm.

[0111] Separately, 89 parts by weight of natural graphite and 9 parts by weight of silicon particles (Si purity: >99.8%, average particle size: 0.9~1.1㎛) as cathode active materials and 2 parts by weight of styrene butadiene rubber (SBR) as a binder were prepared, and a cathode forming slurry was prepared in the same manner as the anode forming slurry. The prepared cathode forming slurry was applied to one side of a copper current collector, then dried at 100°C and rolled to manufacture a cathode. At this time, the total thickness of the cathode composite layer was 150㎛, and the total thickness of the manufactured cathode was approximately 180㎛.

[0112] Then, a separator made of a porous polyethylene (PE) film (thickness: about 16 μm) was interposed between the manufactured anode and cathode, and an electrode assembly was manufactured.

[0113] A full-cell type cell was fabricated by loading the manufactured electrode assembly into a pouch-type case and injecting an electrolyte.

[0114] The above electrolyte used was a carbonate-based electrolyte, specifically, a solution containing lithium hexafluorophosphate (LiPF6, 1.0 M) and 2 wt% of additives in a mixture of ethylene carbonate (EC):dimethyl carbonate (DMC):diethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0115] The additives mixed into the electrolyte are as shown in Table 1 below. Each type of additive was mixed into the aforementioned electrolyte, and the voltage at which the decomposition reaction begins (the voltage at which the electrode reacts within the electrolyte) was measured. The measurement results are as shown in Table 1 below.

[0116] division Voltage reacting with the electrode within the electrolyte VC (Vinylene carbonate) 3.0 V PS (1,3-propane soltone) 2.7 V ESa (Ethylene sulfate) 2.5 V PRS (1,3-propene sultone) 2.3 V Vinyl ethylene carbonate (VEC) 1.8 V

[0117] Based on the voltage at which the additive reacts with the electrode in the electrolyte, the additives were classified into first and second additives. As first additives, VEC, PRS, and ESa were classified, with a voltage at which they react with the electrode in the electrolyte of 2.5 V or less. As second additives, PS and VC were classified.

[0118] The electrolyte injection conditions for each example are shown in Table 2 below.

[0119] division 1st electrolyte injection Secondary electrolyte injection Injection volume (V / V%) Types of additives Injection volume (V / V%) Types of additives Example 1 80% VEC, PRS, PS, VC 20% PS, VC Example 2 70% VEC, PRS, ESa 30% PS, VC Example 3 50% VEC, PRS 50% PS, VC Example 4 35% VEC, PRS 65% PS, VC Comparative example 100% VEC, PRS, PS, VC - -

[0120] In Table 2, Examples 1 to 4 injected the electrolyte in two separate injections. The first electrolyte injection was performed under conditions where the battery voltage was 2.5 V, with the SOC charged to approximately 10%. In Comparative Example 1, the entire electrolyte was injected without performing an initial charge on the battery. Additionally, the total content of the additives was controlled to 2% by weight relative to the electrolyte, and each additive was uniformly mixed.

[0121] In the case of Example 1, during the first injection of the electrolyte, PS and VC, classified as second additives, were mixed and injected together with VEC and PRS, classified as first additives. In Example 1, 80% was injected during the first injection of the electrolyte, and the remaining 20% ​​was injected during the second injection of the electrolyte.

[0122] In the case of Example 2, 70% of the total amount of the electrolyte containing VEC, PRS, and ESa, classified as the first additive, was injected during the first electrolyte injection. Then, the remaining 30% was injected during the second electrolyte injection.

[0123] In the case of Example 3, 50% of the total amount of an electrolyte containing VEC and PRS, classified as the first additive, was injected during the first electrolyte injection. Then, the remaining 50% was injected during the second electrolyte injection.

[0124] In the case of Example 4, 35% of the total amount of an electrolyte containing VEC and PRS, classified as the first additive, was injected during the first electrolyte injection. Then, the remaining 65% was injected during the second electrolyte injection.

[0125] In the case of the comparative example, the electrolyte containing VEC, PRS, PS, and VC as additives was filled all at once.

[0127] In addition, for the batteries of Examples 1 to 4, a gas removal step was performed after the first injection of the electrolyte, and a second injection of the electrolyte was performed. In the case of the Comparative Example, a gas removal step was performed after charging to an SOC level of 10% after the electrolyte injection.

[0129] Experimental Example

[0130] For the secondary batteries manufactured in each example and comparative example, the capacity retention rate after 500 charges and discharges was evaluated.

[0131] Specifically, the secondary batteries prepared in Examples 1-4 and Comparative Examples were charged at a temperature of 25°C with a charging current of 0.05C to a charging cutoff voltage of 4.2 to 4.25 V, and then activated by charging from 0.02 V until the current density reached 0.01C. Afterward, they were discharged with a discharge current of 0.05C to a cutoff voltage of 2 V, and the electrode resistance and the initial charge / discharge capacity per unit mass were measured.

[0132] Then, the capacity during charge-discharge was measured while repeating 500 charge-discharge cycles at 45°C under 0.3°C conditions, and the charge-discharge capacity retention rate was calculated after 500 charge-discharge cycles. The results are shown in Table 2 below.

[0133] division Capacity retention rate after 500 charge-discharge cycles Example 1 87.6% Example 2 90.2% Example 3 85.3% Example 4 82.5% Comparative example 78.9%

[0134] As shown in Table 3 above, the secondary batteries of Examples 1 to 4 show a capacity retention rate of 80% or more, and show a higher capacity retention rate compared to the secondary battery of the Comparative Example.

[0135] However, in the case of Example 4, only 35% of the electrolyte was injected during the first injection, followed by a gas removal step, and then the second injection of the electrolyte was performed. In this case, the amount of residual gas inside the battery increased, which resulted in a decrease in capacity retention rate.

[0137] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and technical scope of the invention as described in the claims set forth below.

[0138] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

Claim 1 A first electrolyte injection step of injecting a first electrolyte containing a first additive into a battery case housing an electrode assembly and charging the battery to an SOC of S1%; a degas step of removing gas generated inside the battery; a second electrolyte injection step of injecting a second electrolyte containing a second additive into a battery case housing an electrode assembly and charging the battery to an SOC of S2%; A method for manufacturing a secondary battery comprising an activation step and satisfying the following condition 1: [Condition 1] SOC S2% > SOC S1%, wherein the first additive has a voltage range of 1.5 to 2.5V that reacts with the electrode in the electrolyte and includes at least one of VEC (Vinyl ethylene carbonate) and PRS (1,3-propane soltone), and the second additive has a voltage range of 2.5V to 4.2V that reacts with the electrode in the electrolyte and includes at least one of PS (1,3-propane soltone) and VC (Vnylene carbonate). Claim 2 A method for manufacturing a secondary battery according to claim 1, wherein in the first electrolyte injection step, the electrolyte injection rate is in the range of 40 to 95% (V / V). Claim 3 A method for manufacturing a secondary battery according to claim 1, wherein one or more of the first and second electrolytes comprise a non-aqueous organic solvent. Claim 4 A method for manufacturing a secondary battery according to claim 3, wherein the non-aqueous organic solvent is a carbonate-based organic solvent comprising one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). Claim 5 A method for manufacturing a secondary battery according to claim 1, characterized in that the secondary battery is a pouch-type lithium secondary battery. Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 delete Claim 10 delete Claim 11 delete

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