static void Main()
        {
            var sw = Stopwatch.StartNew();

            using (SpreadsheetDocument xl =
                SpreadsheetDocument.Create("LargeFile.xlsx", SpreadsheetDocumentType.Workbook))
            {
                List<OpenXmlAttribute> oxa;
                OpenXmlWriter oxw;

                xl.AddWorkbookPart();
                WorksheetPart wsp = xl.WorkbookPart.AddNewPart<WorksheetPart>();

                oxw = OpenXmlWriter.Create(wsp);
                oxw.WriteStartElement(new Worksheet());
                oxw.WriteStartElement(new SheetData());

                for (int i = 1; i <= 50000; ++i)
                {
                    oxa = new List<OpenXmlAttribute>();
                    // this is the row index
                    oxa.Add(new OpenXmlAttribute("r", null, i.ToString()));

                    oxw.WriteStartElement(new Row(), oxa);

                    for (int j = 1; j <= 100; ++j)
                    {
                        oxa = new List<OpenXmlAttribute>();
                        // this is the data type ("t"), with CellValues.String ("str")
                        oxa.Add(new OpenXmlAttribute("t", null, "str"));

                        // it's suggested you also have the cell reference, but
                        // you'll have to calculate the correct cell reference yourself.
                        // Here's an example:
                        //oxa.Add(new OpenXmlAttribute("r", null, "A1"));

                        oxw.WriteStartElement(new Cell(), oxa);

                        oxw.WriteElement(new CellValue(string.Format("R{0}C{1}", i, j)));

                        // this is for Cell
                        oxw.WriteEndElement();
                    }

                    // this is for Row
                    oxw.WriteEndElement();
                }

                // this is for SheetData
                oxw.WriteEndElement();
                // this is for Worksheet
                oxw.WriteEndElement();
                oxw.Close();

                oxw = OpenXmlWriter.Create(xl.WorkbookPart);
                oxw.WriteStartElement(new Workbook());
                oxw.WriteStartElement(new Sheets());

                // you can use object initialisers like this only when the properties
                // are actual properties. SDK classes sometimes have property-like properties
                // but are actually classes. For example, the Cell class has the CellValue
                // "property" but is actually a child class internally.
                // If the properties correspond to actual XML attributes, then you're fine.
                oxw.WriteElement(new Sheet()
                {
                    Name = "Sheet1",
                    SheetId = 1,
                    Id = xl.WorkbookPart.GetIdOfPart(wsp)
                });

                // this is for Sheets
                oxw.WriteEndElement();
                // this is for Workbook
                oxw.WriteEndElement();
                oxw.Close();

                xl.Close();
            }

            sw.Stop();
            Console.WriteLine(sw.Elapsed);
            Console.ReadLine();
        }

                        //oxw.WriteElement(new CellValue(string.Format("R{0}C{1}", i, j)));
                        oxw.WriteElement(new CellValue("111"));