METHOD FOR PRODUCING A SECONDARY BATTERY WITH NON-AQUEOUS ELECTROLYTE

Abstract

A manufacturing process for a secondary battery with a non-aqueous electrolyte, comprising: preparing a battery assembly (1) in which an electrode body (20) and a non-aqueous electrolyte (30) are included in a battery casing (10); and performing an initial charge in the battery assembly (1), wherein during the initial charge a differential capacity curve of the battery assembly (1) has a first peak voltage (V1) at which a first layer is formed on the electrode body (20), and a second peak voltage (V2) which is higher than the first peak voltage (V1) and at which a second layer is formed on the electrode body (20), the initial charge comprising;Forming the first layer by stopping charging for an initial stop time after charging to a first specified voltage (PV1) set between the first peak voltage (V1) and the second peak voltage (V2), wherein the initial stop time during first layer formation is 2 to 30 seconds, and forming the second layer by charging the battery arrangement (1) to a second specified voltage (PV2) set higher than the second peak voltage (V2) after the first layer has been formed.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention The invention relates to a manufacturing process for a secondary battery with non-aqueous electrolyte, in which an initial charging step is carried out for a battery arrangement. 2. Explanation of the state of the art In recent years, non-aqueous secondary batteries, such as lithium-ion and nickel-hydride batteries, have been primarily used as portable power supplies for PCs and mobile devices, and as power sources for vehicles. The manufacturing process for these non-aqueous secondary batteries typically involves providing a battery assembly containing an electrode body and a non-aqueous electrolyte within a battery casing. This assembly then undergoes an initial charging (conditioning) step, which activates the power-generating elements (electrode body and non-aqueous electrolyte) and creates a non-aqueous secondary battery. When the initial charging step is performed, a portion of the solvent in the non-aqueous electrolyte is decomposed, forming a solid electrolyte interface (SEI) on the surface of the electrode (usually the negative one). The appropriately formed SEI layer suppresses the internal resistance and improves the performance characteristics. Unexamined Japanese patent applications JP 2016-149211A and JP 2016-15280A include examples of a method for appropriately forming the SEI layer. Furthermore, unexamined Japanese patent application JP 2001-176560A discloses a method in which an initial charging step is performed, followed by a first adjustment step in which charge and discharge cycles are repeated and which includes a stop step to stabilize battery characteristics in a short time. For example, JP 2016-149 211 A describes a technique for the initial charging of a cell (battery array) to a preset specific voltage. In JP 2016-149 211 A, the specific voltage is set during initial charging based on a peak voltage indicated in a differential capacity curve observed during charging. If multiple peak voltages are observed in the differential capacity curve, then, according to the procedure described in JP 2016-149 211 A, multiple specific voltages are set based on each peak voltage, and constant current / constant voltage charging (CCCV charging) is performed stepwise from a low voltage to a high voltage based on these specific voltages.In this way, constant-voltage charging (CCCV charging) can be performed at a decomposition voltage for each material (precursor of the SEI layer), allowing the SEI layer to be formed with high accuracy. JP 2001 - 325 988 A relates to a method for charging a secondary battery with a non-aqueous electrolyte and aims to reduce the amount of current required for film formation, thereby improving initial charge and discharge efficiency. JP 2014 - 232 704 A relates to a secondary battery coated with a layer containing sulfur atoms on the positive electrode and a layer containing boron and / or phosphorus atoms on the negative electrode. BRIEF EXPLANATION OF THE INVENTION According to the method described in JP 2016-149211A, a high-performance secondary battery with a non-aqueous electrolyte can be produced by forming a suitable SEI layer. However, given the recent increase in demand for improved performance characteristics in the field of secondary batteries with non-aqueous electrolytes, the further development of a technique capable of forming a more suitable SEI layer is being pursued. The invention provides a manufacturing method capable of forming a suitable SEI layer in a first charging step and producing a high-performance secondary battery with a non-aqueous electrolyte. This objective is achieved by the subject matter of the independent claim. Further developments of the invention are the subject matter of the dependent claims. The manufacturing process according to a first aspect of the invention comprises providing a battery assembly in which an electrode body and a non-aqueous electrolyte are contained in a battery housing, and performing an initial charging of the battery assembly. During the initial charging, a differential capacity curve of the battery assembly exhibits a first peak voltage at which a first layer is formed on the electrode body, and a second peak voltage, which is higher than the first peak voltage, at which a second layer is formed on the electrode body.The initial charging process comprises forming the first layer by halting charging for an initial stop time after charging to a first specific voltage, set between the first peak voltage and the second peak voltage, and forming a second layer by charging to a second specific voltage, set higher than the second peak voltage after the first layer has been formed. The "differential capacitance curve" in this description is defined in a diagram showing the relationship between the voltage and a differential capacitance (dQ / dV) obtained by differentiating the charge / discharge capacitance with respect to the voltage. In the first-layer formation step of the manufacturing process disclosed in the invention, charging is stopped for a predetermined time after a first defined voltage has been reached. This makes it possible to quickly reduce any overvoltage in the first-layer formation step, thereby preventing the first and second layers from forming simultaneously. As a result, both the first and second layers can be formed with high accuracy without a significant reduction in manufacturing efficiency. Therefore, a high-performance secondary battery with a non-aqueous electrolyte and a correspondingly formed SEI layer can be efficiently manufactured. According to the first aspect of the invention, the initial stop time during the formation of the first layer is 2 to 30 seconds. This allows the overvoltage in the first layer formation step to be reduced appropriately in a short time. According to the first aspect of the invention, charging can be stopped for a second stop time during the formation of the second layer, after charging has reached the second defined voltage. Experiments have demonstrated that a secondary battery with a non-aqueous electrolyte can be produced with higher performance by stopping charging during the second-layer formation step as described above. According to the first aspect of the invention, the second stop time during the formation of the second layer can be from 2 to 30 seconds. In this way, a secondary battery with a non-aqueous electrolyte and higher performance can be efficiently manufactured. According to the first aspect of the invention, the non-aqueous electrolyte can comprise a film-forming agent and a solvent. The first layer can be a solid electrolyte interface (SEI) formed by decomposition of the film-forming agent. The second layer can be an SEI layer formed by decomposition of the solvent. The performance-enhancing effect of the manufacturing process disclosed in the invention is particularly evident when a non-aqueous electrolyte comprising such a film-forming agent is used. According to the first aspect of the invention, the layer-forming agent can be lithium bis(oxalate)borate (LiBOB). LiBOB can form a particularly suitable SEI layer under various layer-forming agents and contribute to improving performance characteristics. According to the first aspect of the invention, the formation of the first layer can comprise performing constant-current (CC) charging, in which a voltage is increased until it reaches the first specified voltage, and performing constant-voltage (CV) charging, in which the voltage is held at the first specified voltage for a predetermined time. In the first-layer formation step, by performing CCCV charging, which comprises both CC charging and CV charging, the charging to the first specified voltage can be carried out stably, thus enabling the straightforward formation of a suitable SEI layer. According to the first aspect of the invention, the formation of the second layer can include performing constant-current (CC) charging, in which a voltage is increased until it reaches the second specified voltage, and constant-voltage (CV) charging, in which the voltage is held at the second specified voltage for a predetermined time. Furthermore, in the second layer formation step, the charging can be carried out stably by performing constant-current, constant-voltage, constant-voltage (CCCV) charging, so that a suitable SEI layer can be easily formed. BRIEF EXPLANATION OF THE DRAWINGS Features, advantages, and the technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which identical symbols denote identical elements, and wherein Fig. 1 is a flowchart showing steps of a manufacturing process according to an embodiment of the invention; Fig. 2 is a front view schematically showing the internal structure of a battery arrangement produced according to the manufacturing process of the embodiment of the invention; Fig. 3 is a diagram showing a differential capacity curve when the battery arrangement is charged; Fig. 4 is a diagram showing a change over time of a charging current and a charging voltage in an initial charging step of the manufacturing process according to the embodiment of the invention; and Fig.5 is a diagram showing the relationship between a stopping time (sec) and a power (W) of samples 1 to 13. DETAILED EXPLANATION OF EXECUTION FORMS The inventors of the invention conducted various experiments and studies. The following describes the studies carried out by the inventors. As described above, in the prior art, a plurality of specific voltages are set based on each peak voltage, and a charging voltage is incrementally increased based on these specific voltages when a plurality of peak voltages are observed in a differential capacitance curve. For example, if two peak voltages are observed, charging to a first specific voltage and subsequently charging to a second specific voltage allows two types of solid electrolyte interface (SEI) precursors to decompose individually. By conducting various studies to form a more suitable SEI layer, the inventors have determined that the above technique is improvable.In particular, the inventors discovered that the precursor, which is supposed to decompose by charging to the second specified voltage, can decompose during charging to the first specified voltage, potentially leading to a deterioration in the formation accuracy of the SEI layer. Presumably, this is due to an overvoltage occurring during charging to the first specified voltage, causing two types of precursors to decompose simultaneously. To improve the aforementioned condition, the inventors investigated means for reducing the overvoltage during charging to the first specified voltage and for suppressing the simultaneous decomposition of two or more precursors. As a means of reducing the overvoltage, a method for maintaining low-current charging for a long time after reaching the first specified voltage could be considered. However, the application of this method could lengthen the initial charging step and significantly reduce manufacturing efficiency. Therefore, the inventors conducted further studies and concluded that temporarily stopping the charging process after charging to the first specified voltage was the best course of action.As a result of conducting various experiments, the inventors have found that, since the overvoltage is quickly reduced by stopping the charging process, it is possible to suppress a deterioration in the formation accuracy of the SEI layer without causing a significant deterioration in manufacturing efficiency. The manufacturing process for a non-aqueous electrolyte disclosed in the invention (hereinafter also referred to simply as the "manufacturing process") is based on the foregoing findings. The following describes embodiments of the invention. Elements or steps that differ from those mentioned in the invention and are necessary for its implementation can be understood as a matter of design for competent persons based on the relevant prior art. The invention can be implemented on the basis of the content disclosed in this description and general technical knowledge in the field. A. First embodiment The following describes a manufacturing process for a lithium-ion secondary battery as an embodiment of a manufacturing process for a secondary battery with a non-aqueous electrolyte disclosed in the invention. Fig. 1 is a flowchart showing a manufacturing process according to the first embodiment of the invention. As shown in Fig. 1, the manufacturing process according to the present embodiment comprises an arrangement provision step S10 and an initial charging step S20. The steps are described individually below. 1. Order provisioning step S10 In the manufacturing process according to the present embodiment, an arrangement provisioning step S10 is first carried out to provide a battery arrangement in which an electrode body and a non-aqueous electrolyte are contained in a battery housing. The "battery arrangement" in this description refers to a secondary battery with a non-aqueous electrolyte prior to activation by initial charging. In this step, a battery arrangement can be manufactured based on a known method, or a pre-manufactured battery arrangement can be provided. Fig. 2 is a front view schematically showing an internal structure of the battery assembly produced according to the present embodiment. As shown in Fig. 2, a battery assembly 1 is produced by accommodating an electrode body 20 and a non-aqueous electrolyte 30 in a battery housing 10. Each component of the battery assembly 1 is described below. Battery housing The battery housing 10 is a flat, rectangular container made of a metal material such as aluminum, stainless steel, nickel-plated steel, or similar. The battery housing 10 consists of a housing body 12 and a lid 14. The housing body 12 is a flat, box-shaped container with an opening at the top. The lid 14 is a plate-shaped element that closes the opening at the top of the housing body 12. A positive electrode terminal 16 and a negative electrode terminal 18 are attached to the lid 14. Electrode body The electrode body 20 in the present embodiment is a wound electrode body. Such a wound electrode body is produced by stacking long plate- or sheet-shaped electrodes (a positive electrode and a negative electrode) with a separator arranged between them and winding the stack. A positive electrode connection section 22, formed by winding only one positive electrode current collector, is provided at one end of the electrode body 20 in a lateral direction X of the electrode body 20, and a negative electrode connection section 24, formed by winding only one negative electrode current collector, is provided at the other end of the electrode body 20 in the lateral direction X of the electrode body 20. A positive electrode terminal 16 is connected to the positive electrode connection section 22, and a negative electrode terminal 18 is connected to the negative electrode connection section 24.A detailed description of the elements comprising the electrode body 20 (normally a positive electrode, a negative electrode, and a separator) is omitted because the elements used in a general lithium-ion secondary battery can be used without particular restriction, and the elements comprising the electrode body 20 do not characterize the technology disclosed in the invention. Furthermore, the structure of the electrode body 20 is not limited to the wound electrode body described above, and any structure that can be used as the electrode body of a general secondary battery can be used without particular restriction. Another example of the structure of the electrode body 20 is a stacked electrode body in which a plurality of positive electrodes, negative electrodes, and separators are stacked. Non-aqueous electrolyte The non-aqueous electrolyte 30 is contained within the battery housing 10 together with the electrode body 20. In Fig. 2, a portion of the non-aqueous electrolyte 30 has penetrated the electrode body 20 (normally between the positive and negative electrodes), with the remaining non-aqueous electrolyte 30 located outside the electrode body 20. The injected quantity of the non-aqueous electrolyte 30 is not particularly limited and can be so large that all of the non-aqueous electrolyte 30 penetrates the electrode body 20. The non-aqueous electrolyte 30 in the present embodiment comprises a carrier salt, a film-forming agent, and a solvent. For example, a lithium salt is used as the carrier salt. Specific examples of the carrier salt are lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), lithium bis(fluorosulfonyl)imide (Li(FSO2)2N), and lithium trifluoromethanesulfonate (LiCF3SO3). The non-aqueous electrolyte 30 can comprise two or more types of the carrier salt described above. The concentration of the carrier salt in the non-aqueous electrolyte 30 is preferably, for example, about 0.5 to 2.0 mol / l. The film former uses a compound that decomposes at a lower voltage than other components (usually the solvent) of the non-aqueous electrolyte 30 and forms a SEI layer on the surface of an electrode (usually a negative electrode). The addition of this film former to the non-aqueous electrolyte 30 suppresses degradation of battery capacity due to solvent decomposition, and a suitable SEI layer can be formed. Examples of such a film former include lithium bis(oxalate)borate (LiBOB:LiB(C₂O₄)₂), lithium difluorooxalate borate (LiBF₂(C₂O₄)), lithium difluorobis(oxalate)phosphate (LiPF₂(C₂O₄)₂), lithium difluorophosphate (LiPO₂F₂), vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), ethylene sulfite (ES), and propane sultone (PS).The non-aqueous electrolyte 30 may comprise only one type of the film-forming agent described above, or two or more types. Of the film-forming agents described above, LiBOB is preferred because it allows the formation of a particularly suitable SEI layer. To effectively suppress solvent decomposition, the concentration of the film-forming agent in the non-aqueous electrolyte 30 is preferably 0.02 wt.% or more, more preferably 0.1 wt.% or more, and further preferably 0.3 wt.% or more. Conversely, to suppress the residue of the film-forming agent after the initial charging step, the upper limit of the concentration of the film-forming agent is preferably 3 wt.% or less, more preferably 2 wt.% or less, and further preferably 1 wt.% or less. A non-aqueous solvent capable of dissolving the support salt and the film-forming agent described above can be used. Examples of such solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and butylbutyrolactone (BL), as well as chain-linked carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Only one type of the non-aqueous solvents described above, or a mixed solvent consisting of two or more types of non-aqueous solvents blended together, can be used. If a mixed solvent is used, a mixture of cyclic and chain-linked carbonates is preferred. This allows both the electrical conductivity and the electrochemical stability of the non-aqueous electrolyte to be achieved at a high level.Preferred examples of such a mixed solvent are a mixed solvent of EC, DMC and EMC. Peak voltage Fig. 3 is a diagram showing a differential capacitance curve when the battery arrangement is charged. As shown in Fig. 3, the differential capacitance curve observed during the initial charging of the battery arrangement 1 used in the present embodiment exhibits a first peak voltage V1, at which a first layer forms on the electrode body, and a second peak voltage V2, which is higher than the first peak voltage V1 and at which a second layer forms on the electrode body. The vertical axis or ordinate in Fig. 3 shows the "differential capacitance (dQ / dV)" and the horizontal axis or abscissa the "voltage (V)". The "differential capacitance (dQ / dV)" indicates the amount of change in capacitance per unit voltage.The differential capacitance (dQ / dV) serves as an index indicating the rate of a film-forming reaction in which the precursor, such as the film-forming agent or solvent, decomposes to form a SEI layer. Specifically, assuming the battery's internal resistance is constant, the voltage during constant-current (CC) charging changes depending on the degree of film formation. That is, when the voltage exceeds the voltage (peak voltage) at which the differential capacitance (dQ / dV) increases, the rate of film formation also increases. The "differential capacitance curve" in this description is represented by a graph showing the relationship between the voltage and the differential capacitance (dQ / dV), which is obtained by differentiating the charge / discharge capacity with the voltage. Such a differential capacitance curve can, for example, be...based on the method disclosed in JP 2016-149211A. As shown in the differential capacity curve in Fig. 3, the differential capacity curve when charging the battery arrangement 1 using the non-aqueous electrolyte 30, which comprises the film former and the solvent, shows, for example, a first peak voltage V1 when the first layer is formed from the film former, which decomposes at a relatively low voltage (about 1.8 V in Fig. 3), and a second peak voltage V2 when the second layer is formed from the solvent, which decomposes at a higher voltage than the film former (about 2.9 V in Fig. 3). 2. Initial charging step S20 In the initial charging step S20, the battery assembly 1 described above is charged for the first time. This "initial charging" refers to the process of charging the battery assembly before a current-generating element is activated, so that the voltage is gradually increased within a voltage range (0 V to 4 V in the present embodiment) used after the battery assembly has been manufactured. The initial charging activates the current-generating elements (usually the electrode body 20 and the non-aqueous electrolyte 30) of the battery assembly 1. In addition, the precursors of the SEI layer (e.g., the film former and the solvent) present in the battery housing 10 are decomposed, and the SEI layer is formed on the electrode body (usually the negative electrode). As shown in Fig. 1, the initial charging step S20 of the manufacturing process according to the present embodiment comprises a first-layer formation step S22 and a second-layer formation step S24. In the present embodiment, a full charging step S26 is carried out after the second-layer formation step S24. Fig. 4 is a diagram showing the time-dependent changes of a charging current (A) and a charging voltage (V) in the initial charging step, including the steps described above. First layer formation step S22 In the initial charging step S20 of the present embodiment, a first-layer formation step S22 is performed first. In step S22, after charging to a first determined voltage PV1, which lies between the first peak voltage V1 and the second peak voltage V2, the charging is stopped for a predetermined time. As described above, in the first-layer formation step S22, the first defined voltage PV1 is initially set between the first peak voltage V1 and the second peak voltage V2 in the differential capacitance curve (see Fig. 3), and, as shown in Fig. 4, charging with the first defined voltage PV1 is carried out. In this process, the precursor (the layer-forming agent in the present embodiment), which decomposes at a relatively low voltage, is preferably decomposed to form the first layer. The first defined voltage PV1 is preferably set between a peak-maximum voltage and a peak-limit voltage of the first peak voltage V1. This allows for the formation of a more suitable first layer. In this description, the "peak-maximum voltage" refers to a voltage at which the differential capacitance (dQ / dV) is highest at the first peak voltage V1 (1.8 V in Fig. 3).The "peak-end voltage" refers to the voltage at which the differential capacitance (dQ / dV) begins to rise again towards the second peak voltage V2 (2.2 V in Fig. 3) after the differential capacitance (dQ / dV) falls from the peak voltage. That is, the first specified voltage PV1 can be set in a range of 1.75 V or more and less than 2.9 V when considering the differential capacitance curve as shown in Fig. 3. However, to form a preferred first layer, the first specified voltage PV1 is set in a range of 1.8 V or more and 2.2 V or less. The charging performed in the first-layer formation step S22 is preferably a constant-current / constant-voltage charging (CCCV charging) as shown in Fig. 4. Specifically, in the first-layer formation step S22, CC charging is carried out until the voltage reaches the first defined voltage PV1, and after reaching the first defined voltage PV1, constant-voltage charging (CV charging) is continued for a predetermined time. This allows the charging to the first defined voltage PV1 to be carried out stably and a suitable first layer to be formed easily. With regard to suitable first-layer formation, the CCCV charging time in the first-layer formation step S22 is preferably one second or more, more preferably five seconds or more, further preferably 15 seconds or more, and most preferably 20 seconds or more.With a view to improving manufacturing efficiency, the upper limit of the loading time is preferably 100 seconds or less, more preferably 70 seconds or less, further preferably 50 seconds or less, and particularly preferably 40 seconds or less. Subsequently, in the first-layer formation step S22 of the present embodiment, charging is stopped after the first defined voltage PV1 described above has been reached, with the initial stop time during first-layer formation being 2 to 30 seconds. As shown in Fig. 4, the formation of the first layer (decomposition of the layer-forming agent) continues even during the charging stop, so that the voltage drops from the first defined voltage PV1 and the overvoltage is rapidly reduced. Thus, in the first-layer formation step S22, simultaneous formation of the first and second layers is suppressed, and the first layer is formed with high accuracy. As shown in Fig. 4, the charging current during the charging stop is normally 0 A. It should be noted that Fig. 4 does not indicate that any unwanted low-level current flow during the charging stop is eliminated. Furthermore, the stop time in the first-layer formation step S22 can be suitably varied depending on the material of the non-aqueous electrolyte, the setting of the initial voltage PV1, and similar factors. For example, the stop time in the first-layer formation step S22 is two seconds or more to appropriately reduce the overvoltage. Moreover, the inventors have demonstrated experimentally that post-production performance improves particularly significantly when charging in the first-layer formation step S22 is stopped for five seconds or more. However, the upper limit of the stop time is not strictly limited and can be 30 seconds or less. It has also been shown that the performance improvement effect is saturated if charging is stopped for more than a certain period.Taking this point into account, the upper limit of the stop time is 30 seconds or less, more preferably 20 seconds or less, and more preferably 15 seconds or less. Second shift formation step S24 In the present embodiment, in the first charging step S20, following the first-layer formation step S22, a second-layer formation step S24 is performed to charge to a second specified voltage PV2, which is set higher than the second peak voltage V2. Thus, the precursor (solvent in the present embodiment), which decomposes at a voltage equal to or higher than the second peak voltage V2, decomposes to form the second layer. The second specified voltage PV2 is preferably set to a voltage higher than the final peak voltage (3.0 V in Fig. 3) of the second peak voltage V2. That is, considering the differential capacitance curve as shown in Fig. 3, the second specified voltage PV2 can be set within a range of 2.9 V or more, although it is preferably set to 3.0 V or more to form a more desirable second layer.The upper limit of the second defined voltage PV2 is not specifically limited and only needs to be lower than the voltage in the fully charged state (4.0 V in the present embodiment). For example, the upper limit of the second defined voltage PV2 is set to 3.18 V. As in the first-layer formation step S22, it is preferred to also perform CCCV charging in the second-layer formation step S24. Specifically, as shown in Fig. 4, in the second-layer formation step S24, CC charging is performed until the voltage reaches the second defined voltage PV2, and CV charging is continued for a predetermined time after the second defined voltage PV2 has been reached. In this way, the second layer can be formed easily. For more convenient formation of the second layer, the CCCV charging time in the second-layer formation step S24 is preferably 60 seconds or more, more preferably 90 seconds or more, and further preferably 100 seconds or more, more preferably 120 seconds or more.With regard to suppressing a deterioration in manufacturing efficiency, the upper limit of the loading time in the second layer formation stage S24 is preferably 300 seconds or less, more preferably 270 seconds or less, further preferably 210 seconds or less, and particularly preferably 180 seconds or less. In the manufacturing process according to the present embodiment, charging to the second defined voltage PV2 is carried out in the second layer formation step S24, and then the charging is stopped. It has been experimentally confirmed that this improves the performance characteristics of the manufactured secondary battery. Although it is not intended to restrict the technology disclosed in the invention, it is assumed that the performance improvement is achieved by stopping the charging in the second layer formation step S24 because the overvoltage in the second layer formation step S24 is reduced and excessive solvent decomposition is suppressed. If the charging stop is carried out in the second layer formation step S24, the stop time is preferably set to one second or more, and more preferably to two seconds or more.Experiments have demonstrated that a charging stop of five seconds or more can result in improved performance. Considering manufacturing efficiency, the upper limit of the stop time in the second-layer formation step S24 is preferably 30 seconds or less, more preferably 25 seconds or less, further preferably 20 seconds or less, and most preferably 15 seconds or less. Full charging step S26 In the manufacturing process according to the present embodiment, the full charging step S26 is carried out after the second-layer formation step S24. In the full charging step S26, a specific full charging voltage PV3 (4.0 V in Fig. 4) is set based on a standard of the manufactured secondary battery with non-aqueous electrolyte, and constant current (CC) charging is carried out until the voltage reaches the specified full charging voltage PV3. Subsequently, in the full charging step S26, the charging is switched to constant voltage (CV) charging after the voltage reaches the voltage PV3 specified for full charging, and charging is terminated when the current drops to a cut-off current (1 A in Fig. 4).Although it is not intended to limit the technology disclosed in the invention, the implementation time of the full-load step S26 is preferably 500 seconds or more and 1300 seconds or less, more preferably 600 seconds or more and 1200 seconds or less, more preferably 700 seconds or more and 1100 seconds or less, and particularly preferably 800 seconds or more and 1000 seconds or less. Once the full-charge step S26 described above is complete, charging is carried out across the entire usable voltage range, producing a secondary battery with non-aqueous electrolyte and activated current-generating elements. Since charging is stopped in the first-layer formation step S22 of the manufacturing process according to the present embodiment, the first and second layers can be formed individually with high accuracy. Thus, the secondary battery with non-aqueous electrolyte produced according to the present embodiment has a suitable SEI layer and can exhibit high performance characteristics.Since the overvoltage is rapidly reduced by the charging interruption, the manufacturing efficiency of the present embodiment can be maintained at a higher level than in a manufacturing process where an interrupted current is maintained for a longer period. Therefore, a high-performance secondary battery with a non-aqueous electrolyte and a suitable SEI layer can be efficiently manufactured using the present embodiment's manufacturing process. B. Other embodiments One embodiment (first embodiment) of the manufacturing process disclosed in the invention has been described above. However, the first embodiment described above is not intended to limit the manufacturing process disclosed in the invention, and various modifications can be made to it. In the first embodiment, for example, a battery arrangement with a non-aqueous electrolyte comprising a film former and a solvent is used. By using a non-aqueous electrolyte comprising a film former as described above, a suitable SEI layer can be easily formed. However, the charging objective in the manufacturing process disclosed in the invention is not limited to the embodiment described above. In particular, when a mixed solvent obtained by mixing several non-aqueous solvents is used, several voltage peaks can be displayed in the differential capacitance curve, even without adding the film former.Even when using a battery arrangement with a differential capacity curve exhibiting multiple peak voltages due to the mixed solvent, as described above, an initial charging step can be performed, including a first-layer formation step where charging is carried out taking into account a first peak voltage, and a second-layer formation step where charging is carried out taking into account a second peak voltage. By implementing a charging stop in the first-layer formation step, a high-performance secondary battery with a non-aqueous electrolyte and a suitably formed SEI layer can be efficiently produced. Furthermore, when using a layer former, it is not necessary to add it to the non-aqueous electrolyte. For example, applying a paste or mass containing a layer former to an electrode body material (e.g.,The surface of a separator forms an SEI layer derived from the layer-forming agent. Since a plurality of peak voltages are also specified in the differential capacitance curve, the technique according to the invention can be applied to the case described above. Although the first embodiment is applied to a lithium-ion secondary battery, the manufacturing process disclosed in the invention is not limited to the production of a lithium-ion secondary battery. The invention can be applied to the production of various secondary batteries with non-aqueous electrolyte in which an SEI layer can be formed in the first charging step without any particular restrictions. In the first embodiment, charging is stopped in both the first-layer and second-layer formation steps. However, it has been experimentally confirmed that it is possible to suppress the simultaneous formation of the first and second layers and to produce a high-performance secondary battery with a non-aqueous electrolyte, as long as charging is stopped at least in the first-layer formation step. Thus, cases may also arise in which, with a view to improving manufacturing efficiency, the charging stoppage preferably occurs only in the first-layer formation step. The initial charging step S20 in the first embodiment comprises two layer formation steps: the first layer formation step S22 and the second layer formation step S24. Alternatively, the initial charging step of the manufacturing process disclosed in the invention can comprise three or more layer formation steps. For example, if three peak voltages are observed in the differential capacitance curve, a third layer formation step is preferably provided between the second layer formation step and the full charging step. At this point, the second determined voltage is preferably set between the second peak voltage and the third peak voltage, and the third determined voltage is preferably set to a higher voltage than the third peak voltage. In this way, each of the first to third layers can be formed individually, and a suitable SEI layer can be formed.Furthermore, when performing the third layer formation step, charging is preferably stopped during the second layer formation step. This prevents the second and third layers from being formed simultaneously, thus enabling the formation of a more suitable SEI layer. Stopping charging during the third layer formation step is also preferred for improving post-production performance characteristics. Although a detailed description is omitted to avoid repetition, when performing four or more layer formation steps, charging is preferably stopped in each layer formation step after charging has been carried out at the specified voltage. Experimental examples The following are examples of experiments related to the invention. These examples are not intended to limit the scope of the invention. 1. Preparing the battery arrangement A plate-shaped positive electrode using lithium-nickel-cobalt-manganese composite oxide (Li1-xNi1 / 3Co1 / 3Mn1 / 3O2) as the positive electrode active material and a plate-shaped negative electrode using graphite as the negative electrode active material were fabricated. A separator (porous polyolefin film) was also prepared. These sheet and plate elements were then stacked and wound to form an electrode body. Next, a carrier salt (LiPF6) at a concentration of 0.1 mol / L was added to a solvent mixture comprising ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC : DMC : EMC = 30 : 40 : 30 to prepare a non-aqueous electrolyte. In this experiment, a film former (LiBOB) at a concentration of 0.5 wt% was added to the non-aqueous electrolyte.The electrode body was then placed in an aluminum battery housing, and subsequently the non-aqueous electrolyte was poured into the housing, thus providing a battery assembly for evaluation. 2. Preparation of the samples Sample 1 The initial charging was performed in the aforementioned battery setup based on the following procedure to prepare a lithium-ion secondary battery for the experiment (Sample 1). First-layer charging step: Using the first specified voltage of 2.2 V, constant current (CC) charging was performed until the voltage reached the first specified voltage, and then constant voltage (CV) charging was maintained for 30 seconds. Second-layer charging step: After the first-layer charging step was completed, CC charging was performed until the voltage reached the second specified voltage (3.18 V), and then CV charging was maintained for 150 seconds. Full charge step: After the second-layer charging step was completed, CC charging was performed at 20 A until the voltage reached the full charge voltage (4 V), then the charging mode was switched to CV charging and charging was continued until the current reached the final current (1 A). Samples 2 to 5 The experimental lithium-ion secondary batteries (Samples 2 to 5) were provided under the same conditions as in Sample 1, except that charging was stopped to allow the current to drop to 0 A after constant voltage (CV) charging in each of the first-layer and second-layer formation steps. The stop time was set to two seconds for Sample 2, five seconds for Sample 3, 20 seconds for Sample 4, and 30 seconds for Sample 5. Samples 6 to 9 The experimental lithium-ion secondary batteries (Samples 6 to 9) were prepared under the same conditions as Sample 1, except that charging was stopped after CV charging in the first-layer formation step. The stop time was set to two seconds for Sample 6, five seconds for Sample 7, 20 seconds for Sample 8, and 30 seconds for Sample 9. Samples 10 to 13 The experimental lithium-ion secondary batteries (samples 10 to 13) were prepared under the same conditions as in sample 1, except that charging was stopped after CV charging in the second-layer formation step. The stop time was set to two seconds for sample 10, five seconds for sample 11, 20 seconds for sample 12, and 30 seconds for sample 13. 2. Evaluation attempts The performance of the prepared samples was measured. Specifically, under temperature conditions of -35 °C, a constant current (CC) discharge at C / 5 was performed on the lithium-ion secondary battery for evaluation, and the performance was measured after adjusting the state of charge (SOC) to 30%. The results of the performance measurements of the samples are shown in Fig. 5. As shown in Fig. 5, samples 2 to 13, in which the charging was stopped in one of the first layer formation steps and in the second layer formation step, had improved performance characteristics compared to sample 1, in which the charging stop was not performed. Comparing samples 2 to 13, in which the charging stop was performed, the highest performance was observed in samples 2 to 5, where the charging stop was performed in both the first and second-shift formation steps. Samples 6 to 9, in which the charging stop was performed in the first-shift formation step, exhibited higher performance than samples 10 to 13, in which the charging stop was performed in the second-shift formation step. These results indicate that the performance improvement effect of the charging stop is more pronounced when the charging stop is performed in the first-shift formation step. This is presumably due to the fact that the overvoltage is reduced by the charging stop, and simultaneous formation of the first and second shifts is suppressed. A comparison of the stop times of samples 2 to 13 also revealed that the performance improvement effect of the charging stop occurred at a stop time of two seconds or more. Furthermore, it was found that setting the stop time to five seconds or more showed a more suitable effect in improving performance. Since, on the other hand, the performance improvement effect was saturated with a stop time of more than 20 seconds, it can be assumed that the upper limit of the stop time, taking manufacturing efficiency into account, should preferably be set at 30 seconds or less. Although specific examples of the invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims comprises various modifications and alterations of the specific examples given above.

Claims

A manufacturing process for a secondary battery with a non-aqueous electrolyte, comprising: preparing a battery assembly (1) in which an electrode body (20) and a non-aqueous electrolyte (30) are included in a battery casing (10); and performing an initial charge in the battery assembly (1), wherein during the initial charge a differential capacity curve of the battery assembly (1) has a first peak voltage (V1) at which a first layer is formed on the electrode body (20), and a second peak voltage (V2) which is higher than the first peak voltage (V1) and at which a second layer is formed on the electrode body (20), the initial charge comprising;Forming the first layer by stopping charging for an initial stop time after charging to a first specified voltage (PV1) set between the first peak voltage (V1) and the second peak voltage (V2), wherein the initial stop time during first layer formation is 2 to 30 seconds, and forming the second layer by charging the battery arrangement (1) to a second specified voltage (PV2) set higher than the second peak voltage (V2) after the first layer has been formed. Manufacturing method according to claim 1, wherein, during the formation of the second layer, the charging is stopped for a second stop time after charging to the second determined voltage (PV2). Manufacturing method according to claim 2, wherein the second stop time during the formation of the second layer is 2 to 30 seconds. Manufacturing process according to any one of claims 1 to 3, wherein the non-aqueous electrolyte comprises a film former and a solvent, the first layer is a solid electrolyte interface formed by decomposition of the film former, and the second layer is a solid electrolyte interface formed by decomposition of the solvent. Manufacturing process according to claim 4, wherein the layer former is lithium bis(oxalate)borate. Manufacturing method according to any one of claims 1 to 5, comprising forming the first layer; performing a constant current charge in which a voltage is increased until it reaches the first determined voltage (PV1), and performing a constant voltage charge in which the voltage is held at the first determined voltage (PV1) for a predetermined time. Manufacturing method according to any one of claims 1 to 6, comprising forming the second layer; performing a constant current charge in which a voltage is increased until it reaches the second specified voltage (PV2), and performing a constant voltage charge in which the voltage is held at the second specified voltage (PV2) for a predetermined time.

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