JP2015026559A - Method for manufacturing nonaqueous electrolytic secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a nonaqueous electrolyte secondary battery capable of rapidly producing enough gas to activate CID even after repetition of charge and discharge, the safety of which is further ensured.SOLUTION: A method for manufacturing a nonaqueous electrolyte secondary battery comprises a positive electrode active material-preparing process for preparing a positive electrode active material, provided that the nonaqueous electrolyte secondary battery has: a positive electrode including the positive electrode active material consisting of a lithium transition metal oxide containing calcium and transition metals including at least nickel, cobalt and manganese; a negative electrode; a nonaqueous electrolytic solution containing an overcharge additive agent which produces gas at overcharge; and a current interruption device(CID) mechanism for interrupting a conducting path when a pressure inside the battery is equal to or larger than a predetermined value. The positive electrode active material-preparing process includes the following steps of: (a) preparing a nickel-cobalt-manganese complex hydroxide; and (b) baking a mixture of the prepared nickel-cobalt-manganese complex hydroxide, a calcium peroxide, and a lithium salt.

Description

  The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery including a pressure-sensitive current interrupting device (CID).

  Nonaqueous electrolyte secondary batteries such as lithium secondary batteries are preferably used for so-called portable power supplies, high-output power supplies mounted on vehicles, and the like because they are lighter and have higher energy density than existing batteries. Such a nonaqueous electrolyte secondary battery is generally used in a controlled state so as to be within a predetermined voltage range. However, when an excessive current is supplied to the battery due to an erroneous operation or the like and the battery is overcharged, there is a possibility that problems such as decomposition of the electrolyte and generation of gas in the battery case may occur. Therefore, for the purpose of preventing such problems and obtaining higher safety, a battery provided with a current interruption mechanism (CID) that interrupts current when an increase in battery internal pressure associated with an overcharge state is detected has been proposed. (For example, refer to Patent Document 1). Further, in order to quickly realize the operation of CID at the time of overcharge, an overcharge additive that is oxidized and decomposed to generate gas at the time of overcharge is also added to the non-aqueous electrolyte.

JP 2013-080627 A JP 2012-252964 A

By the way, an overcharge additive such as cyclohexylbenzene (CHB) or biphenyl (BP) activates a polymerization reaction on the surface of the positive electrode active material during overcharge, and generates hydrogen gas. However, as the battery is repeatedly charged and discharged, the polymerization reaction of the anti-charge additive is suppressed, and oxidative decomposition is less likely to occur. That is, even if the battery is overcharged, the oxidative decomposition reaction of the gas generating additive at the positive electrode does not proceed rapidly, and it is difficult to ensure the amount of gas necessary for CID operation at an early stage.
The present invention has been made in view of such circumstances, and a purpose thereof is to promptly generate a gas amount capable of operating CID even after repeated charging and discharging, and a non-aqueous electrolyte with more safety secured. It is providing the manufacturing method of a secondary battery.

This invention provides the manufacturing method of a nonaqueous electrolyte secondary battery as what solves the said subject. Such a non-aqueous electrolyte secondary battery has a positive electrode including a positive electrode active material, a negative electrode, a non-aqueous electrolyte containing an overcharge additive that generates gas when overcharged, and a conductive path when a pressure inside the battery exceeds a predetermined value. A current interruption mechanism is provided. The positive electrode active material contains calcium (Ca) and contains at least nickel (Ni), cobalt (Co), and manganese (Mn) as transition metals, a lithium transition metal oxide (hereinafter simply referred to as “Ca-containing Li”). (NCM) oxide ”).
And in this manufacturing method, the said positive electrode active material is prepared by the positive electrode active material preparation process including the following process (a) (b), It is characterized by the above-mentioned.
(A) Prepare a nickel-cobalt-manganese composite hydroxide (hereinafter sometimes referred to as “NCM composite hydroxide”).
(B) Firing a mixture of the prepared (NCM) composite hydroxide, calcium peroxide (CaO ₂ ), and lithium salt.

As described above, in the present invention, the Ca component contained in the positive electrode active material is added in the form of calcium peroxide (CaO ₂ ) and at the time of firing the NCM composite hydroxide and the Li compound. ing. According to this configuration, Ca is almost uniformly incorporated into the crystal structure of the Ca-containing Li (NCM) oxide that is the positive electrode active material, and at the same time, a compound of Li and CaO is deposited on the surface of the positive electrode active material. Li existing on the surface of the positive electrode active material generally exists in the form of LiOH, and the surface of the positive electrode active material is alkalinized in the non-aqueous electrolyte. However, unlike LiOH, a compound of Li and CaO (for example, LiCaO or the like) does not become an alkaline component, and this is considered to reduce the suppression of polymerization of the antistatic additive on the positive electrode surface. Thereby, even after repeated charging / discharging, the gas generation efficiency on the surface of the positive electrode during overcharge is maintained high, and the amount of gas necessary for the operation of the CID can be secured early.

In a preferred embodiment of the method for producing a non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous electrolyte includes at least one of cyclohexylbenzene and biphenyl as an overcharge additive, and the total of these is from 2% by mass to It is included at a ratio of 6% by mass. And the said positive electrode active material is characterized by including a calcium (Ca) component in the ratio of 0.2 mol%-0.3 mol%.
With this configuration, the amount of gas necessary for the operation of the CID can be ensured, and the content of the overcharge additive can be appropriately suppressed to a small amount. A decrease in capacity can be suppressed.

  The nonaqueous electrolyte secondary battery manufactured by the manufacturing method disclosed herein ensures safety during overcharge for a long period even when charging / discharging at a high rate (particularly, a high rate cycle). Can be a thing. Taking advantage of such characteristics, the manufacturing method disclosed herein can be suitably applied when manufacturing a non-aqueous electrolyte secondary battery for applications that require high power density and high durability. Examples of such applications include power sources (vehicle driving power sources) such as electric vehicles and hybrid vehicles. In other words, the present invention can also provide a vehicle including the nonaqueous electrolyte secondary battery as another aspect. Note that the battery mounted on the vehicle may be in the form of an assembled battery in which a plurality of the batteries are electrically connected to each other.

It is a flowchart which shows the preparation process of the positive electrode active material which concerns on one Embodiment. It is the graph which illustrated the relationship between the charge condition of the nonaqueous electrolyte secondary battery before and after an endurance test, and a battery case internal pressure. It is a flowchart which shows the preparation process of the conventional positive electrode active material.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than the matters particularly mentioned in the present specification (for example, the preparation process of the positive electrode active material and the blending amount of the overcharge additive) and the matters necessary for the implementation of the present invention (for example, the battery structure and the battery) The general manufacturing process, etc.) can be grasped as a design matter of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

As described above, the method disclosed herein is to manufacture a positive electrode including a positive electrode active material, a negative electrode, a non-aqueous electrolyte including an overcharge additive, and a non-aqueous electrolyte secondary battery including a CID. Here, the positive electrode active material is a Ca-containing Li (NCM) oxide. And this manufacturing method essentially comprises a positive electrode active material, (a) a step of preparing an NCM composite hydroxide, and (b) a step of firing a mixture of the composite hydroxide, calcium peroxide and lithium salt. It is characterized by preparing by the positive electrode active material preparation process to include. The method for producing the Ca-containing Li (NCM) oxide is disclosed in detail, for example, in Patent Document 2 by the present applicants. The present invention is disclosed in Patent Document 2 in that CaO ₂ is used as a Ca source and that the Ca source is required to be mixed at the time of firing a mixture of a NiCoMn composite hydroxide and a lithium salt. It is clearly distinguished from technology. Regarding other points, the present invention can include the disclosure of Patent Document 2 as a reference. FIG. 1 is a flowchart illustrating a positive electrode active material preparation step according to an embodiment of the present invention. Hereinafter, the positive electrode active material preparation step will be described in order with reference to FIG.

[A: Positive electrode active material preparation step]
(A) Preparation process of NCM composite hydroxide First, about lithium transition metal oxide containing calcium (Ca) which is a positive electrode active material and containing at least nickel, cobalt and manganese as transition metals, Ca component and Li component An aqueous solution containing a metal component other than (typically a transition metal component) is prepared, and a transition metal hydroxide is crystallized from the aqueous solution. Here, the ratio of each transition metal element in the transition metal hydroxide can be preferably matched with the ratio (stoichiometry) of the transition metal element in the target Ca-containing NCM oxide. In addition, in this Ca containing NCM oxide, transition metal elements other than Ni, Co, and Mn can be included as a transition metal. For example, the composition of a Ca-containing NCM oxide is represented by the following general formula:
_{LixNi a Co b Mn c Mt d} Ca e O 2 (1)
(Where, 0.95 ≦ x ≦ 1.05, 0.8 ≦ a + b + c + d ≦ 1.2, a × b × c ≠ 0, 0 ≦ d ≦ 0.05, (x + a + b + c + d + e + 2) × 0 .1 ≦ e ≦ (x + a + b + c + d + e + 2) × 0.5)
The transition metal element Mt other than Ni, Co, and Mn is not particularly limited. For example, one or two of Sc, Ti, V, Fe, Zr, Mo, Pd, Ta, and W are used. The above can be considered.
The aqueous solution containing a transition metal can be prepared by dissolving a salt containing a desired transition metal in an aqueous solvent so that the ratio of each transition metal is a desired ratio. Such transition metal salts may be, for example, sulfates, nitrates, chlorides, and the like. The transition metal may form a complex in an aqueous solution. As for the concentration of the transition metal aqueous solution, the total of all transition metals (Ni, Co, Mn, etc.) is preferably about 1 to 2.2 mol / L. The aqueous solvent used in preparing such an aqueous solution is typically water, and water containing a reagent (acid, base, etc.) that improves solubility may be used depending on the solubility of each salt used. .

  Next, the NCM composite hydroxide is crystallized by neutralizing the aqueous solution of the transition metal under pH control. For neutralization, it is convenient to mix a basic aqueous solution with an aqueous solution of a transition metal. The basic aqueous solution contains a strong base (such as an alkali metal hydroxide) and a weak base (such as ammonia). When a predetermined amount of an aqueous solution containing a transition metal is prepared, the pH at a liquid temperature of 25 ° C. is 11 to 11. What is maintained at about 14 and does not inhibit the production of NCM composite hydroxide can be preferably used. Typically, a mixed solution of an aqueous sodium hydroxide solution and aqueous ammonia can be used. This mixed solution is preferably prepared so that the pH is in the range of 11 to 14 (for example, about pH 12) and the ammonia concentration is 3 to 25 g / L. Thereby, an NCM composite hydroxide can be obtained in the mixed aqueous solution. The obtained NCM composite hydroxide can be washed with water, filtered and dried after crystallization, and can be prepared into particles having a desired particle size (including crushing, grinding, sieving, classification, etc.). .

(B) Firing step of mixture of NCM composite hydroxide, CaO ₂ and Li salt Typically, a mixture of the NCM composite oxide prepared above, CaO ₂ as a Ca source, and an appropriate lithium salt is typically used. A Ca-containing NCM composite oxide can be prepared by firing in air. As said lithium salt, the general lithium salt used for formation of lithium complex oxide can be especially used without a restriction | limiting. Specific examples include lithium carbonate and lithium hydroxide. These lithium salts can be used alone or in combination of two or more. The mixing ratio of the NCM composite oxide, CaO ₂ and lithium salt may be adjusted so that the ratio of each constituent element excluding oxygen (O) is the same as the ratio in the target Ca-containing NCM composite oxide. . The mixing is preferably performed until each material is in a uniform mixed state.
The firing temperature is preferably in the range of about 700 to 1000 ° C. Firing may be performed at the same temperature at a time, or may be performed stepwise at different temperatures. The firing time can be appropriately selected. For example, after firing at about 700 to 800 ° C. for about 1 to 12 hours, firing at about 800 to 1000 ° C. for about 2 to 24 hours is exemplified. The Ca-containing NCM oxide thus obtained can be adjusted to a desired particle size by adjusting (including crushing, crushing, sieving, classification, etc.) as necessary. A preferable average particle size (which may be a secondary particle size) as the positive electrode active material may be, for example, about 3 μm to 7 μm. The specific surface area is preferably in the range of 0.5 to 1.8 m ² / g.

  The Ca-containing NCM oxide thus prepared is essentially in the form of secondary particles in which primary particles of a Ca-containing NCM composite oxide having a layered structure are gathered. And Ca can exist substantially uniformly in the crystal structure of the primary particles. For example, it is considered to exist uniformly in the form of CaO or the like. In addition, on the crystal surface of the primary particles, Ca forms a compound with Li and exists in a form different from that in the crystal structure of the primary particles. That is, Ca is precipitated by forming a compound of Ca and Li at the grain boundary between primary particles. With such a configuration, for example, even after repeated charging and discharging, high gas generation performance can be maintained without suppressing decomposition of the overcharge additive on the surface of the positive electrode active material. As a result, for example, as shown in FIG. 2 (a), the amount of gas capable of operating the CID can be promptly generated both before and after repeated charging / discharging, and in a safer state (for example, lower SOC) In the state), the conductive path of the non-aqueous electrolyte secondary battery can be blocked.

  The existence form of each component in such a positive electrode active material is, for example, energy dispersive X-ray spectroscopy (EDX) equipped with a transmission electron microscope (TEM) for the obtained Ca-containing NCM composite oxide (secondary particles). It can be grasped by examining the element distribution using Energy Dispersive X-ray Spectroscopy or examining the element surface and chemical state of the particle surface by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

For example, in a calcium-containing lithium transition metal composite oxide obtained by using a calcium sulfide, hydroxide, carbonate or the like as a Ca source by a conventional crystallization method, a calcium component used as a raw material (for example, , Calcium sulfate (CaSO ₄ ) can be distinguished from the Ca-containing NCM composite oxide in that it tends to segregate at grain boundaries. In addition, in the calcium-containing lithium transition metal composite oxide obtained by the conventional method, the Li component is often present in the form of LiOH that can be easily ionized on the surface of the primary particles. It can be distinguished from the Ca-containing NCM complex oxide. In the calcium-containing lithium transition metal composite oxide according to the conventional method, precipitation of a compound of Ca and Li can be seen at the grain boundary between the primary particles. However, such an amount can be a relatively low amount (ratio) than the amount found in the Ca-containing NCM composite oxide. Further, according to the conventional method, it is difficult for Ca to be present almost uniformly as CaO or the like in the crystal structure of the primary particles. Therefore, for example, after repeated charging and discharging, the decomposition reaction of the overcharge additive on the surface of the positive electrode active material is suppressed, and it takes a long time to generate a predetermined amount of gas. As a result, for example, as shown in FIG. 2 (b), it takes more time to operate the CID than before repeated charging / discharging, and the CID is only in a state in which overcharge has progressed more (eg, in a higher SOC state). May not be able to operate.

[B: Battery construction process]
Next, a method for constructing the nonaqueous electrolyte secondary battery in the present invention will be described together with the battery configuration. In addition, since this battery construction process does not characterize this invention, it is only demonstrated briefly based on a typical example. A non-aqueous electrolyte secondary battery is typically constructed by preparing an electrode body having a positive electrode and a negative electrode facing each other, and housing the electrode body and the non-aqueous electrolyte in a battery case. it can.
Here, the positive electrode of the electrode body is typically electrically connected to a positive electrode external connection terminal disposed outside the battery case via a positive electrode current collecting terminal. Moreover, the negative electrode of the electrode body is typically electrically connected to a negative electrode external connection terminal disposed outside the battery case via a negative electrode current collecting terminal. Typically, the positive and negative external connection terminals are arranged on the lid of the battery case, and the electrode body is fixed to the lid as described above, so that electricity can be smoothly input and output, and the battery The position in the case is stabilized. After the electrode body is inserted into the case main body of the battery case, the opening of the case main body is closed by the lid body, and the main part of the electrode body is realized. As the battery case, for example, a lightweight metal case such as an aluminum alloy can be preferably used. The battery case (typically a lid) has a safety valve that communicates with the outside of the case when the internal pressure of the battery case exceeds a predetermined value, a liquid injection port for injecting an electrolyte, and a liquid injection port for sealing the same. A stopper or the like may be provided. Typically, a CID that operates when the internal pressure of the battery case exceeds a predetermined value is provided between the external connection terminal and the current collecting terminal. As long as the CID can block the conductive path at a predetermined operating pressure, the specific configuration or the like is not limited.

An electrode body can be comprised by laminating | stacking typically the positive electrode which has a positive electrode active material layer, and the negative electrode which has a negative electrode active material layer through a separator, for example. For example, the positive electrode and the negative electrode may constitute a laminated electrode body in which a plurality of positive electrodes and negative electrodes are laminated, or constitute a wound electrode body obtained by laminating and winding a long positive electrode sheet and a negative electrode sheet. You may do it. The capacity ratio (C _N / C _P ) calculated as the initial capacity ratio of the positive and negative electrodes, that is, the ratio of the initial charge capacity (C _N ) of the negative electrode to the initial charge capacity (C _P ) of the positive electrode is not particularly limited, For example, it can be set to about 1.0 to 2.1.

As the positive electrode, typically, a positive electrode active material can be used in the form of a positive electrode active material layer formed by adhering a positive electrode active material as a composition together with a conductive material, a binder, or the like onto a positive electrode current collector. The positive electrode current collector includes at least the Ca-containing NCM composite oxide prepared by the positive electrode active material preparation step. In addition, it is a preferable form to use only said Ca containing NCM complex oxide as a positive electrode active material, since the characteristic of this invention becomes clear. However, as long as the object of the present invention is not impaired, other layered and spinel-based lithium composite metal oxides (for example, LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _{1 / 3 Mn 1/3 O 2, LiNi 0.5} Mn 1.5 O 4, LiCrMnO 4, LiFePO 4 , etc.) and the like may be mixed or incorporated into the positive electrode active material. As the conductive material, a carbon material such as carbon black (for example, acetylene black or ketjen black) can be employed. As the binder, various polymer materials such as polyvinylidene fluoride (PVdF) and polyethylene oxide (PEO) can be adopted.

  As the negative electrode, it is possible to use a negative electrode active material layer in which a negative electrode active material is deposited on a negative electrode current collector as a composition together with a binder or the like. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper) can be suitably used. As the negative electrode active material, for example, a carbon material such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), etc. can be used. A material whose surface is coated with amorphous carbon can be suitably employed. As the binder, for example, various polymer materials such as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polytetrafluoroethylene (PTFE) can be adopted.

As the separator, for example, a microporous resin sheet made of a resin such as polyethylene (PE) or polypropylene (PP) can be suitably used. Note that in a battery using a solid electrolyte (lithium polymer battery), the electrolyte may also serve as a separator.
As the non-aqueous electrolyte, typically, a non-aqueous solvent containing a supporting salt can be used. As the supporting salt, for example, a lithium salt, a sodium salt, a magnesium salt, or the like can be used, and among them, a lithium salt such as LiPF ₆ or LiBF ₄ can be preferably used. As the non-aqueous solvent, for example, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones can be used. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be preferably used.

  Such a non-aqueous electrolyte contains an overcharge additive in addition to the above-described non-aqueous solvent and supporting salt. Such an overcharge additive can be used without particular limitation as long as it is a compound that generates gas during overcharge. Especially, it is preferable that any one of cyclohexylbenzene (CHB) and biphenyl (BP) is included. These cyclohexylbenzenes and biphenyls are easy to take a conjugated system and are easy to exchange electrons. For this reason, it is suitably oxidized and decomposed during overcharge, and a large amount of hydrogen gas can be generated. Therefore, the CID can be operated more quickly, and the reliability of the battery can be improved. Furthermore, by using an overcharge additive having a high gas generating ability as described above, the amount of overcharge additive added can be reduced as compared with the conventional case, and the internal resistance of the battery can be reduced. In addition to the above film forming agent, for example, various additives such as a gas generating agent can be appropriately added to the nonaqueous electrolyte.

Next, the non-aqueous electrolyte secondary battery constructed as described above can be provided as a product having a predetermined charge / discharge performance after performing an appropriate conditioning process or aging process.
The non-aqueous electrolyte secondary battery manufactured by the method disclosed herein is difficult to suppress the decomposition of the overcharge additive on the surface of the positive electrode even after the charge / discharge cycle, and the rapid CID operation is performed for a long time. Can be reserved. Therefore, it can be particularly suitably used for non-aqueous electrolyte secondary batteries for various applications that require safety over a long period of time. Among them, high capacity type batteries having a theoretical capacity of about 10 to 100 Ah, batteries for applications that repeatedly charge and discharge at a high rate, and the like, such as plug-in hybrid vehicles (PHV), are specifically mounted. It may be a power source (drive power source) for a motor.

In producing a lithium secondary battery, first, a positive electrode active material was prepared by the following procedure 1 according to the present invention and conventional procedures 2 and 3.
[Procedure 1]
<Example 1>
About half of the water was placed in the reaction vessel and heated to 40 ° C. with stirring. After replacing the reaction vessel with nitrogen, an appropriate amount of 3.25% aqueous sodium hydroxide solution and 25% aqueous ammonia was added in a nitrogen stream, and the pH at the liquid temperature of 25 ° C. was 12.0, and the ammonia concentration in the liquid phase was 20 g. / L was adjusted to obtain a basic aqueous solution.
Nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ), and manganese sulfate (MnSO ₄ ) were dissolved in water so that the molar ratio of Ni, Co, and Mn was a predetermined ratio to prepare a NiCoMn aqueous solution.
The NiCoMn aqueous solution prepared above was added to the basic aqueous solution while maintaining the pH at 12.0 and mixed to crystallize the NiCoMn hydroxide. The crystallized product was filtered, and the alkaline component was washed and dried to obtain the target NiCoMn composite hydroxide.

When the total number of moles of all transition metals (ie, Ni, Co, Mn) in the NiCoMn composite hydroxide is M, the molar ratio of lithium to M (Li / M) is 1.0. Lithium carbonate (Li ₂ CO ₃ ) was weighed as above, and calcium peroxide (CaO ₂ ) was weighed out so that the amount of Ca in the positive electrode active material was 0.3 mol%. The product particles were mixed uniformly. The obtained mixture was baked at 760 ° C. for 4 hours in the air, and then baked at 950 ° C. for 10 hours to obtain a Ca-containing Li (NiCoMn) composite oxide.

<Example 2>
In Example 1 described above, calcium peroxide (CaO ₂ ) was weighed and added so that the amount of Ca in the positive electrode active material was 0.2 mol%. Others were the same as in Example 1 to obtain a Ca-containing Li (NiCoMn) composite oxide.

[Procedure 2]
<Example 3>
About half of the water was placed in the reaction vessel and heated to 40 ° C. with stirring. After replacing the reaction vessel with nitrogen, an appropriate amount of 3.25% aqueous sodium hydroxide solution and 25% aqueous ammonia was added in a nitrogen stream, and the pH at the liquid temperature of 25 ° C. was 12.0, and the ammonia concentration in the liquid phase was 20 g. / L was adjusted to obtain a basic aqueous solution.
Nickel sulfate (NiSO ₄ ), cobalt sulfate (CoSO ₄ ), manganese sulfate (MnSO ₄ ), calcium sulfate (CaSO ₄ ) at a predetermined molar ratio of Ni, Co, and Mn, and in the positive electrode active material A Ca-containing NiCoMn aqueous solution was prepared by dissolving in water such that the Ca amount was 0.3 mol%.
The Ca-containing NiCoMn aqueous solution prepared above was added to the basic aqueous solution while maintaining the pH at 12.0 and mixed to crystallize Ca-containing NiCoMn hydroxide. The crystallized product was filtered, and the alkali component was washed and dried to obtain the target Ca-containing NiCoMn composite hydroxide.

When the total number of moles of all transition metals (ie, Ni, Co, Mn) in the Ca-containing NiCoMn composite hydroxide is M, the molar ratio of lithium to M (Li / M) is 1.0. Lithium carbonate (Li ₂ CO ₃ ) was weighed so as to be uniformly mixed with the Ca-containing hydroxide particles after the heat treatment. The obtained mixture was baked at 760 ° C. for 4 hours in the air, and then baked at 950 ° C. for 10 hours to obtain a Ca-containing Li (NiCoMn) composite oxide.

<Example 4>
In Example 3 above, calcium sulfate (CaSO ₄ ) was weighed and added so that the amount of Ca in the positive electrode active material was 0.2 mol%. Others were the same as in Example 3 to obtain a Ca-containing Li (NiCoMn) composite oxide.

[Procedure 3]
<Example 5>
In the above procedure 1 or 2, the Li (NiCoMn) composite oxide was obtained in the same manner without adding the Ca component to the positive electrode active material.

  Using the Li (NiCoMn) composite oxide prepared in Examples 1 to 5 as the positive electrode active material, acetylene black (AB) and graphite (KS4) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder Was mixed with N-methylpyrrolidone (NMP) such that the mass ratio was 91: 3: 3: 3 to prepare a slurry composition. This composition was applied to a long aluminum foil (positive electrode current collector) having a thickness of about 15 μm to form a positive electrode active material layer. The obtained positive electrode was dried and pressed to produce a sheet-like positive electrode (positive electrode sheet).

  Next, ion exchange of amorphous coated graphite powder as a negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) is performed so that the mass ratio becomes 98.3: 1.0: 0.7. A slurry-like composition was prepared by mixing with water. This composition was applied to a long copper foil (negative electrode current collector) having a thickness of about 10 μm to form a negative electrode active material layer. The obtained negative electrode was dried and pressed to prepare a sheet-like negative electrode (negative electrode sheet).

Next, the positive electrode sheet and the negative electrode sheet produced as described above were passed through a separator (here, a three-layer structure in which a polypropylene (PP) layer was laminated on both sides of a polyethylene (PE) layer was used). The resulting wound electrode body was formed into a flat shape by crushing it from the side and dragging it. And the positive electrode terminal was joined to the edge part of the positive electrode collector of this winding electrode body, and the negative electrode terminal was joined to the edge part of the negative electrode collector, respectively. The positive electrode terminal is provided with a pressure-sensitive CID mechanism in the conductive path.
This electrode body was accommodated in a battery case and a non-aqueous electrolyte was injected. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3: 4: 3, and LiPF ₆ as an electrolyte is about It melt | dissolved by the density | concentration of 1 mol / L, Furthermore, CHB and BP which were adjusted and added so that these total might become the value shown in following Table 1 as an overcharge additive were used. Then, a total of 40 lithium secondary batteries were constructed by attaching a lid to the opening of the battery case and welding and joining. The capacity ratio (C _N / C _P ) of these lithium secondary batteries is adjusted to 1.36, and the rated capacity is 25 Ah.

[Conditioning] The lithium secondary battery was subjected to a conditioning process in which a constant current (CC) charge was performed up to SOC 85% at 1C at 25C. Then, the capacity | capacitance when CC discharge to 3.0V with the discharge rate of 1 / 5C was made into the initial stage capacity | capacitance.

[Evaluation of Initial Gas Generation Amount] The initial gas generation amount was evaluated for 20 batteries among the batteries of Examples 1 to 5 prepared above. That is, the operating state of the CID when charging at constant current (CC) up to SOC 140% at 1C at 25 ° C. is confirmed. If the CID does not operate, the gas pressure in the battery case at that time is measured, and the result is initialized. The gas pressure is shown in Table 1 below. At the same time, the initial resistance between the positive and negative electrodes was measured, and the results are shown in Table 1 below.

[Evaluation of Capacity Maintenance Rate] Among the batteries prepared in Examples 1 to 5, the remaining 20 batteries were constant current up to 4.1 V at a rate of 1/5 C in an environment at a temperature of 25 ° C. (CC) After charging, constant voltage (CV) charging was performed until the current value reached 1/50 C, and a fully charged state was obtained.
Subsequently, after leaving each battery in a thermostat set at 60 ° C. for 2 hours or more, the following charge / discharge operations (1) to (2) were repeated 500 cycles (endurance test).
(1) CC charge to 4.1V at a rate of 2C and rest for 10 minutes.
(2) CC discharge to 3.0 V at a rate of 2 C and rest for 10 minutes.
Thereafter, the discharge capacity was measured by the same procedure as the above initial capacity measurement method to obtain the capacity after endurance. The capacity retention rate (%) was calculated as a ratio of the capacity after endurance to the initial capacity ((capacity after endurance / initial capacity) × 100 (%)). The obtained values (capacity maintenance ratio) are shown together in Table 1.

[Evaluation of gas generation after endurance]
For each battery after the endurance test, check the operating status of the CID when CC is charged to SOC 140% at 1C at 25 ° C. If the CID does not work, measure the gas pressure in the battery case at that time. The results are shown as the post-endurance gas pressure in the column of Table 1 below.

The column relating to the gas pressure in Table 1 shows only the symbol “」 ”when the CID is opened quickly, and the gas pressure and the symbol“ when the CID is delayed without opening. X ".
As shown in Table 1, the operating state of the CID at the initial use stage of the secondary battery was good in any of Examples 1 to 5. The initial capacity of the batteries of Examples 1 to 4 was generally higher than that of Example 5 in which the positive electrode active material did not contain a Ca component.
However, the operating state of the CID after the endurance test is confirmed to be defective in the battery of Example 5 in which the positive electrode active material does not include the Ca component and the battery of Example 3 including the positive electrode active material in which the Ca component is included by the conventional method. As a result, it was confirmed that the overcharge additive was not decomposed and gas was not generated satisfactorily by repeated charge and discharge. In addition, the battery of Example 3 had a higher internal resistance and a lower capacity retention rate than the battery of Example 5.

On the other hand, the batteries of Examples 1 and 2 provided with the positive electrode active material containing the Ca component by the method of the present invention can keep the CID operation quickly after the durability test, and are safe against overcharge. It was confirmed that it was higher. In particular, according to the battery of Example 2, it was confirmed that a battery having a relatively low Ca content, a low internal resistance, and a high initial capacity and a high capacity retention rate was realized. In addition, although the battery of Example 4 in which the amount of the overcharge additive was larger than the battery of Example 3 in which the operation failure after durability was confirmed, the CID operated well after the endurance, the amount of the overcharge additive was The result was that the internal resistance was high and the capacity retention rate was the lowest because it was too much.
From the above, since the secondary battery manufactured according to the present invention has a good presence of the Ca component in the positive electrode active material, the amount of gas generated after the cycle can be kept high with a small amount of Ca. Therefore, it turned out that the compounding quantity of an overcharge additive can be reduced, and the outstanding effects that internal resistance is low and a capacity | capacitance maintenance factor are high are expressed.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Claims (2)

A positive electrode comprising a positive electrode active material, wherein the positive electrode active material is a lithium transition metal oxide containing calcium and containing at least nickel, cobalt and manganese as transition metals;
Negative electrode;
A non-aqueous electrolyte containing an overcharge additive that generates gas when overcharged; and a current interruption mechanism that interrupts a conductive path when the pressure inside the battery exceeds a predetermined value;
A non-aqueous electrolyte secondary battery manufacturing method comprising:
The positive electrode active material is subjected to the following steps:
(A) preparing a nickel-cobalt-manganese composite hydroxide;
(B) firing the prepared nickel / cobalt / manganese composite hydroxide, calcium peroxide, and lithium salt;
The manufacturing method prepared by the positive electrode active material preparation process including this. The non-aqueous electrolyte contains at least one of cyclohexylbenzene and biphenyl as an overcharge additive in a ratio of 2 to 6% by mass in total.
The said positive electrode active material is a manufacturing method of Claim 1 which contains a calcium (Ca) component in the ratio of 0.2 mol%-0.3 mol%.

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