Patent ID: 12199313

SUMMARY OF THE INVENTION

In one aspect, the present application provides hermetically sealed higher capacity lithium ion cells, wherein the positive electrode is based on Lithiated Nickel Cobalt Aluminium Oxide (NCA) or Lithiated Nickel Cobalt Manganese Oxide (NCM) and negative electrode is based on graphite.

In another aspect the present application provides a process for the manufacture of hermetically sealed lithium ion cells comprising adopting laser beam welding for stack to intermediate tab and tab to terminal welding.

Yet another aspect of the present application provides a process for the manufacture of hermetically sealed lithium ion cells wherein the terminal sealing employed is a ceramic to metal seal having three ceramic rings with diffusion bonding.

Still another aspect of the present invention provides a process for the manufacture of hermetically sealed lithium ion cells comprising the steps of:a) processing the positive and negative electrodes wherein the positive electrode is based on Lithiated Nickel Cobalt Aluminium Oxide (NCA) or Lithiated Nickel Cobalt Manganese Oxide (NCM) and negative electrode is based on graphite;b) winding of the electrode stack is carried out in a semi-automatic winding machine using a flat mandrel;c) welding of stack to intermediate tab and tab to terminal using laser beam welding; andd) terminal to lid and case to lid welding using laser beam welding.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification are to be understood as being modified in all instances by the term “about”. It is noted that, unless otherwise stated, all percentages given in this specification and appended claims refer to percentages by weight of the total composition.

Thus, before describing the present invention in detail, it is to be understood that this invention is not limited to particularly exemplified systems or method parameters that may of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only, and is not intended to limit the scope of the invention in any manner.

The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the case of conflict, the present document, including definitions will control.

It must be noted that, as used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a “polymer” may include two or more such polymers.

The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

As used herein, the terms “comprising” “including,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to.

In one aspect, the present application provides hermetically sealed lithium ion cells, wherein the positive electrode is based on Lithiated Nickel Cobalt Aluminium Oxide (NCA) or Lithiated Nickel Cobalt Manganese Oxide (NCM) and negative electrode is based on graphite.

The electrode may further comprise conducting diluents at percentage range of 1-10% and polyvinylidene fluoride at percentage range of 4-10%. The composition of negative electrode is a mixture of graphite at percentage range of 85-96% and polyvinylidene fluoride at percentage range of 3-10%. 1-methyl-2-pyrollidinone (NMP) may be used as solvent.

The final thickness of the electrodes ranges from 140-190 μm and 140-200 μm for positive and negative electrodes respectively. NCA or NCM based electrodes provide high specific capacity and good capacity retention. These materials have sloppy discharge curve which helps in predicting the state of charge of the cell. Other cathode materials (eg. LiCoO2, LiFePO4etc.) used in the prior art have somewhat flat discharge and lower specific capacity.

In another aspect the present application provides a process for the manufacture of hermetically sealed higher capacity lithium ion cells comprising adopting laser beam welding for stack to intermediate tab and tab to terminal welding.

Welding of positive tab-terminal assembly to stack may be carried out by keeping the electrode stack with intermediate tabs and heat sinks on welding workstation with positive intermediate tab on the top. The LASER (IR) head may be focused over positive intermediate tab-stack interface. Further, the Argon gas nozzle may be focused over positive intermediate tab-stack interface and laser beam may be applied.

Welding of negative tab-terminal assembly to stack may be carried out by keeping the electrode stack with negative intermediate tabs and heat sinks on welding workstation with negative intermediate tab on the top. The LASER (IR/Green) head may be focused over negative intermediate tab-stack interface. Further, the Argon gas nozzle may be focused over negative intermediate tab-stack interface and laser beam may be applied. Laser power may be 5-8″ kW″. High energy is required for the welding of copper with IR alone due to the high reflectivity and conductivity of copper. Therefore, a combination of IR and Green is used in the present invention. Green laser will be easily absorbed by copper reducing the energy required for welding by IR.

Yet another aspect of the present application provides a process for the manufacture of hermetically sealed lithium ion cells wherein the terminal seal employed is a ceramic to metal seal having three ceramic rings with diffusion bonding. The ceramic to metal seal used in the present invention is based on diffusion bonding of ceramic to metal and is having three ceramic rings. Diffusion bonded seals with three rings have better corrosion resistance and strength and thus improve the leak tightness of the cell over a period of time.

Still another aspect of the present invention provides a process for the manufacture of hermetically sealed lithium ion cells comprising the steps of:a) processing the positive and negative electrodes wherein the positive electrode is based on Lithiated Nickel Cobalt Aluminium Oxide (NCA) or Lithiated Nickel Cobalt Manganese Oxide (NCM) and negative electrode is based on graphite;b) winding of the electrode stack in a semi-automatic winding machine using a flat mandrel;c) welding of stack to intermediate tab and tab to terminal using laser beam welding; andf) terminal to lid and case to lid welding using laser beam welding.

Processing of the electrodes may be carried out by coating the active material slurry of positive electrode based on Lithiated Nickel Cobalt Aluminium Oxide (NCA) or Lithiated Nickel Cobalt Manganese Oxide (NCM) and negative electrode based on graphite on aluminium foil and copper foil respectively. The composition of positive electrode may be NCA/NCM: 80-90%, conducting diluent: 1-10% and Polyvinylidene fluoride: 4-10%. The composition of negative electrode may be mixed graphite: 85-96% and Polyvinylidene fluoride: 3-10%. 1-methyl-2-pyrollidinone (NMP) may be used as solvent for the processing of the electrode slurry for both positive and negative electrodes. The final thickness of the electrodes may be adjusted to 140-190 μm and 140-200 μm for positive and negative electrodes respectively.

In a specific embodiment, one layer of positive electrode (12-16 m) and one layer of negative electrode (12-16 m) along with separator in between may be wound to form the electrode stack. The separator length may range from 14-17 m and width may range from 6-8 mm more than the negative electrode coating width. The winding may be done in such a way that the uncoated areas of positive electrode and negative electrode project from opposite sides of the stack.

The positive substrate projected width may range from 4-12 mm and negative substrate projected width may range from 4 to 14 mm. Welding of positive intermediate tab to positive terminal involves positioning the positive terminal on the positive intermediate tab and focusing LASER head over the positive terminal-tab interface. Welding may be carried out at a peak power of 4-8 kW.

Welding of negative intermediate tab to negative terminal may be carried out by positioning the negative terminal on the negative intermediate tab and focusing LASER head over the negative terminal-tab interface and welding may be carried out at a peak power of 3-8 kW with IR and green laser with power of 1-2 kW.

Fixing of positive tab-terminal assembly to stack may be carried out by dividing the half portion of aluminium bare of stack into three equal groups.

The grouped aluminium foil may be inserted into the grooves of the positive intermediate tab (with the terminals welded on it). The intermediate tab may be crimped. Fixing of negative tab-terminal assembly to stack may be carried out by dividing the half portion of copper bare of stack into three equal groups.

The grouped copper foil may be inserted into the grooves of the negative intermediate tab (with the terminals welded on it). The intermediate tab may then be crimped. Welding of positive tab-terminal assembly to stack may involve keeping the electrode stack with intermediate tabs and heat sinks on welding workstation with positive intermediate tab on the top. Focusing LASER (IR) head over positive intermediate tab-stack interface. Focusing the Argon gas nozzle over positive intermediate tab-stack interface and laser beam may be applied. Once welding is completed, the stack may be taken out from welding station. Laser power may range from 5-8 kW.

Welding of negative tab-terminal assembly to stack may be carried out by keeping the electrode stack with negative intermediate tabs and heat sinks on welding workstation with negative intermediate tab on the top. LASER (IR/Green) head may be focused over negative intermediate tab-stack interface. The Argon gas nozzle may be focused over negative intermediate tab-stack interface and laser beam may be applied. Once welding is completed, the stack may be taken out from welding station. Laser power may range from 5-8″ kW″.

Cell case to lid welding may involve inserting the electrode stack with terminal into the cell case with lip such that the terminals face upward. The lid may be placed such that the two terminals project out through the ports in the lid. LASER head and Argon gas nozzle may be focused over positive terminal seal to lid interface and welding may be carried out. The laser power is 5-8 kW for the welding. LASER head and Argon gas nozzle may be focused over negative terminal seal to lid interface and then welding may be carried out.

The case to lid welding may be carried out by focusing laser head and Argon gas nozzle over case to lid interface and carrying out case to lid welding. The laser power for case to lid welding is 5-8 kW at a feed rate of 0.1-1 mm/s in the linear path and 0.5-1.7 mm/s in the radial path.

In a specific embodiment, there is provided a lip on the case to avoid laser beam penetration during case to lid welding.

225-260 g of electrolyte may be added through the fill port provided on the lid. The cell may further be kept for soaking. The cell is formed, gases vented and the fill port may be welded by laser beam welding to achieve hermeticity. The laser power used is 5-9 kW.

The hermetically sealed lithium ion cells of the present invention have a capacity of 40 to 100 Ah with very high capacity retention for various applications, and have low internal resistance of less than 2 mΩ. Helium leak rate achieved is less than 10−8mbar L/s. The cell manufactured is subjected to charge-discharge cycles for 1800 cycles at 100% depth-of-discharge. The capacity retention is >80% of the initial capacity.

The cells manufactured by the method can be employed for mission critical applications viz. powering satellites, launch vehicles, aircrafts, military vehicles, submarines and electric vehicles.

The following examples are provided to better illustrate the claimed invention and are not to be interpreted in any way as limiting the scope of the invention. All specific materials, and methods described below, fall within the scope of the invention. These specific compositions, materials, and methods are not intended to limit the invention, but merely to illustrate specific embodiments falling within the scope of the invention. One skilled in the art may develop equivalent materials, and methods without the exercise of inventive capacity and without departing from the scope of the invention. It is the intention of the inventors that such variations are included within the scope of the invention.

EXAMPLES

Manufacture of Hermetically Sealed Lithium Ion Cells

Electrode Processing

The active material slurry of positive electrode based on Lithiated Nickel Cobalt Aluminium Oxide (NCA) or Lithiated Nickel Cobalt Manganese Oxide (NCM) and negative electrode based on graphite is coated on aluminium foil and copper foil respectively. The composition of positive electrode is NCA/NCM: 80-90%, conducting diluent: 1-10% and Polyvinylidene fluoride: 4-10%. The composition of negative electrode is mixed graphite: 85-96% and Polyvinylidene fluoride: 3-10%. 1-methyl-2-pyrollidinone (NMP) was used as solvent for the processing of the electrode slurry for both positive and negative electrodes. The final thickness of the electrodes was adjusted to 140-190 μm and 140-200 μm for positive and negative electrodes respectively.

Electrode Stack Winding

The electrode stack is wound in a semi-automatic winding machine using a flat mandrel. One layer of positive electrode (12-16 m) and one layer of negative electrode (12-16 m) along with separator in between is wound to form the electrode stack. The separator length is kept at 14-17 m and width is kept at 6-8 mm more than the negative electrode coating width. The winding is done in such a way that the uncoated areas of positive electrode and negative electrode project from opposite sides of the stack. The positive substrate projected width is 4 to 12 mm and negative substrate projected width is 4 to 14 mm. The negative electrode extends beyond the length and width of the positive electrode.

Cell Assembly

Assembling the cell in humidity controlled environment with RH<1%. The following are the different steps involved in cell assembly.

Welding of Intermediate Tab to Terminals

The positive terminal is positioned on the positive intermediate tab (aluminium) and LASER head is focused over the positive terminal-tab interface and welding is carried out at a peak power of 4-8 kW. The negative terminal is positioned on the nickel plated negative intermediate tab (copper) and LASER head is focused over the negative terminal-tab interface and welding is carried out at a peak power of 3-8 kW with IR and green laser.

Fixing of Tab-Terminal Assembly to Stack

Half portion of aluminium bare of stack is divided into three equal groups. The grouped foils are inserted into the grooves of the positive intermediate tab (with the terminals welded on it). The positive intermediate tab was crimped. Half portion of copper bare of stack is divided into three equal groups. The grouped foils are inserted into the grooves of the Nickel plated negative intermediate tab (with the terminals welded on it). The negative intermediate tab was crimped.

Welding of Tab-Terminal Assembly to Stack

The electrode stack was kept with intermediate tabs and heat sinks on welding workstation with positive intermediate tab on the top. LASER (IR) head was focused over positive intermediate tab-stack interface. The Argon gas nozzle was focused over positive intermediate tab-stack interface and laser beam was applied. Once welding was completed, the stack was taken out from welding station. The stack was kept in the welding workstation with Nickel plated negative intermediate tab on the top. The LASER (IR/Green) head was focused over negative intermediate tab-stack interface and welding was carried out. Once welding was completed, the stack was taken out from welding station. The laser power was 5-8 kW for both weldings.

Terminal to Lid and Cell Case to Lid Welding

The electrode stack with tab-terminal assembly was inserted into the cell case with a lip such that the terminals face upward. The lid was placed such that the two terminals project out through the ports in the lid. The LASER head and Argon gas nozzle were focused over positive terminal seal to lid interface and welding was carried out. The laser power was 5-8 kW for the welding. Similarly, the LASER head and Argon gas nozzle were focused over negative terminal seal to lid interface and welding was carried out. The LASER head and Argon gas nozzle were focused over case to lid interface and case to lid welding was carried out. The laser power for case to lid welding was 5-8 kW at a feed rate of 0.1-1 mm/s in the linear path and 0.5-1.7 mm/s in the radial path.

225-260 g of electrolyte was added through the fill port provided on the lid. After soaking, the cell was formed, gases were vented and the fill port is welded by laser beam welding to achieve hermeticity. The laser power used was 5-9 kW. The Helium leak rate achieved was less than 10−8mbar 1/s.

The cell manufactured in the above manner was subjected to charge-discharge cycles for 1800 cycles at 100% depth-of-discharge. The capacity retention was >80% of the initial capacity.